But let's face it, this valuation of Dropbox cannot be relied on. That $4 billion is mostly derived from fat cat VCs competing for a hot deal. It's far more important to ask: who is using Dropbox currently and is there anything in the use cases that justifies such a high valuation? So I asked the tech-savvy RWW community just that.

1. People now access the Web on multiple devices; including the traditional PC, smartphones, tablets like iPad, Netbooks and more.

2. As Web-connected devices proliferated, it became increasingly useful to use cloud computing services for file management.

Startups have attempted to tap into this huge market opportunity as far back as 2006, when ReadWriteWeb named Sharpcast (now known as SugarSync, a Dropbox competitor) as our Most Promising Company. So Dropbox isn't the only file sync service around. Some of the other products mentioned in my informal survey were SugarSync, Box.net, Ubuntu One and Wuala.

However it's Dropbox that has emerged to become the leading file sync service, since launching to the public in September 2008.

Daily Users

Most of the feedback I gathered from Twitter, Google+ and Facebook indicated that Dropbox is a product that is used not only daily, but multiple times a day. That's always a great sign for a startup.

Mickey Mellen is a heavy Dropbox user. Mellen told me via Google+ that he uses Dropbox about 100 times every day. He has over 40,000 files in his Dropbox account, totalling over 30 GB in size. "It's simply my primary drive," he said. "Every file of mine goes in there, so that every device of mine (desktop, laptop, netbook, tablet, phone) has access to it."

Tori Cushing said that she uses it daily, "all through the day." She has "just about all of the folders on my computer on Dropbox."

Dylan Bland is another daily Dropbox user. He uses it as a "default directory for a lot of important saves." He added, "we also use it at work to share common files."

Campbell Yule tweeted that he uses Dropbox "all the time, many, many times a day." His main use case is "for file sharing across locations."

ReadWriteWeb's own Jon Mitchell is a heavy Dropbox user. "Nearly all my primary workflows sync across devices using Dropbox," Jon remarked. Writing is of course Jon's occupation and he told me that he works "entirely in .txt files that save to a Dropbox directory that I can get to and work on from any device."

David Acklin said that for him, Dropbox is "always running, always backing up."

Both Personal and Business Use

The responses suggested that Dropbox is being used for both personal and business file sharing. Michael Schade uses it to store personal files, although he said that many of his business files have "moved to Google for easier collaboration."

But Dropbox is getting a lot of uptake for business collaboration, too. Ben Kepes said that he uses Dropbox multiple times a day, for "collaborating on docs across timezones and geographies."

Professional photographer Gareth Robins uses it every day for a variety of uses, including a shared folder with his accountant and another with his photographer assistant. He also uses it to deliver photos to his clients. He puts the photos in a Dropbox folder and shares the link with them.

My friend Emily Davidow told me on Facebook that she uses Dropbox "regularly for multiple shared projects."

Less Frequent Users

Others use Dropbox less regularly. I myself am in that camp. I currently use Dropbox to save files (mostly PDFs) that I want to read on my iPad. However I'm interested to expand my usage, now that I've heard how others are using it.

RWW writer (and part-time musician) John Paul Titlow tweeted that he uses Dropbox about weekly, "for household file-sharing, exchanging sound clips w/ bandmates and sending very large files occasionally."

Kim Sherrell told me on Google+ that she uses Dropbox "once in a while." She noted, "I'm reluctant to share resources when I'm editing or working on big files."

Workflow & Ease of Use

As Brian Ries rightly pointed out, how much you use Dropbox depends on how integrated it is in your workflow.

The ease of use of Dropbox was another factor that people commented on. "Dropbox just works," remarked Bill Kirby.

That's an important point, because syncing in the modern Web is too often an irksome process full of glitches. Indeed ever since I "upgraded" to Mac OS X Lion, I've noticed that home sharing (Apple's way of syncing your iTunes account across devices, among other things) has been very buggy.

Like any startup that is scaling up fast, Dropbox has its challenges. Dave Parry, an Assistant Professor at the University of Texas, blogged earlier this year about privacy concerns. But overall, the feedback I gathered from Twitter, Google+ and Facebook was overwhelmingly positive. Many respondents said that they use Dropbox multiple times a day, for both business and personal file sync and sharing.

Big Market - And So Far Dropbox is Delivering...

File sync and sharing is a potentially huge market, which we identified back in 2006 when we named Sharpcast as our Most Promising Company. Dropbox has become the leader in this space, due to its generally frictionless service and excellent usability. Indeed, its usability across multiple devices is probably what has kept it one step ahead of cloud computing giants, such as Amazon, Google and Microsoft.

Whether it's worth $4 billion is another matter. Judging on the product alone though, Dropbox has carved out a great niche and it has a good chance of becoming a very valuable company. Let us know what you think of Dropbox's value, in the comments.

Just before I started writing this, I was attempting to sync data from the online note-taking app Evernote. I had made some notes on my iPad Evernote app while in a cafe, where I didn't have Internet connectivity (I'm a premium subscriber to Evernote, so I have offline access to my data). When I attempted to sync up that content to my Evernote desktop app in my home office, it didn't immediately update. I refreshed... then again... no sync. Perplexed, I moved onto another activity and then checked again 5 minutes later. By then the changes had synced up, but the delay was disconcerting.

However last night I could not get a friend to show as 'online' in imo.im, despite having been chatting with that person moments before using Facebook on my PC. After struggling with this for 5 or so minutes, I switched to Friendly and managed to re-establish contact with my bemused friend. That may've been a bug in imo.im, but regardless it was another example of things not syncing as they should.

How Syncing Across Devices Works

Syncing usually involves using the Internet as the central 'hub' - with apps and/or devices being 'spokes' that connect to the hub. Evernote's approach is fairly typical:

All of your notes (unless stored in a local -- that is, not synchronized -- notebook) are synchronized to Evernote on the Web. Evernote's servers house a copy of all synced notes because all of the Evernote client applications, both mobile and desktop, connect to Evernote on the web to get the latest version of the notes for each user.

Evernote's service and software applications are arranged in what's called a "hub-and-spoke" configuration. This means that every single sync operation that takes place will involve Evernote on the web (the "hub"). For instance, if you initiate a sync from Evernote on your desktop computer, any new or updated content will be uploaded to Evernote on the Web so they'll be ready to be downloaded when any of your other devices initiate a subsequent sync.

Specialist Sync Services

So far we've been talking about sync as a feature of web services, but there are also specialist sync services. Dropbox is probably the most high profile in the consumer market, but another is Sharpcast, which ReadWriteWeb named as our Most Promising Company of 2006.

We chose Sharpcast back in 2006 because it was "solving a big problem (syncing data across Web, desktop and other devices) and also is an integral part of many different trends that will be popular in 2007 and beyond - mobile, rich media, a world of multiple devices, and more."

While we were right about the trend towards multiple Web devices - and that was before the iPhone was unveiled in January 2007 - things haven't quite panned out for Sharpcast. It's not because syncing became unnecessary. In fact it's a must-have feature in all apps that work across devices, particularly those with an offline component such as Evernote and Instapaper. Sharpcast had an opportunity to establish itself as the sync glue for other web apps, but it didn't manage to pull that off. Instead, the likes of Evernote and Instapaper built their own sync solutions.

Sharpcast is still plugging away, but now it competes with Dropbox and others as primarily an online storage service. Sync is one of the main features, but it's no longer enough on its own.

Sync Remains a Problem

Evernote is one of my favorite apps (here's an interview I conducted last year, which outlines how the product was created) and most of the time the sync works well on it. But syncing in this day and age should be completely hidden from the user. I notice some kind of sync issue with Evernote every week or two. It still has work to do.

More generally, I am constantly coming across issues where things don't sync up properly between devices. Skype has probably been the worst offender for me over the years - for example, adding someone as a Skype contact on one computer and then not seeing that person display when you log into another computer. To this day, I continue to come across that 'bug.'

What have been your experiences of sync? More importantly, have you come across any promising new sync solutions?

To enable extension sync in Chrome, you'll first need to install the current developer's build. Once installed, you'll then need to edit the Chrome shortcut's properties.

In Windows, you right-click on the shortcut, choose "Properties," and in the "Target" box, add -enable-sync-extenstions at the end of the command, to the right of the quotes. (Update: see the comments section for a tip on implementing this feature without the reported bugs).

Mac OS X users will need to use Terminal or this handy script that does the work for you (Pointed out to us courtesy of LifeHacker.)

Sync: For a Browser that Knows You

The great thing about Chrome's synchronization options is how it allows you to create a standardized experience no matter what computer you're using. Whether on the netbook in the living room, the desktop in the den or your notebook at the office, you can install Chrome and immediately have it set up with your personal preferences.

For this former Firefox user, the addition of extension sync has been one of the more highly anticipated options, second only to bookmark sync. There was a time - not too long ago, mind you - when you had to make manual lists of your installed extensions or use some sort of third-party add-on to back them up every time Firefox released a new version. And believe me, that process was not as simple as it sounds.

With Chrome, though, the transition from version to version is seamless. There's no backup needed. Forget iterative Web apps, Chrome is the iterative Web browser.

Although the current version of extension sync is still in testing - and apparently a bit crash-prone reports CNET - it's only a matter of time before the feature is stabilized and ported to the beta channel, followed by the public release.

As for what's next for Chrome sync, could it be the ability to sync browser history, searches and cookies? Passwords? Auto-complete settings? We would imagine that it's all of the above...maybe not soon but definitely not never.

Like its progenitor, Memeo Connect still offers drag-and-drop uploads, but in the latest release, the application's operating system integration has been dramatically improved. Most notably, your Google Docs folder now appears as a virtual drive that Memeo labels "GDrive", and, according to company representatives, the name is being used with Google's blessing.

To Internet early adopters, the name "GDrive" rings more than a few bells. It's referring to the long-rumored cloud storage service that Google has yet to launch. In its imagined state, Google's GDrive would have been a lot like Microsoft's SkyDrive: several gigabytes of free storage available on the Web for all your files. On the theoretical GDrive, however, files could be in any format, of any size and there would be easy ways to sync them or move them back and forth between your computer and the cloud. Office files would open with Google's Docs service, an online counterpart to desktop programs like Microsoft Office, and some even imagined that GDrive would further integrate with other Google properties, like Picasa for photos or YouTube for videos.

Google never fully realized everyone's GDrive dreams, but its Google Docs service is functional enough for most. It allows for the upload of any file type while multiple third-party services offer decent options for keeping files in sync between your computers and cloud. These include Memeo competitors like Box.net, Dropbox, Syncplicity, SugarSync, OfficeSync, Gladinet and more.

There are few programs that actually offer the full virtual drive functionality that Memeo now does, though. The company worked closely with Google to build this latest version of its Connect software and when Google engineers found out Memeo was calling the virtual folder it creates "GDrive," they had a good laugh.

Sorry, Internet, Google isn't designing its own GDrive service anytime soon, but it's well aware of the rumors.

Google actually prefers that, when it comes to GDrive-type offerings, third parties do it for them. The closest thing we'll see to a Google-branded tool of any sort is a desktop uploader application now being built, sources tell us. But it's no GDrive, based on what we've heard.

Version 2.0: More OS Integration Blurs Line Between Desktop and Cloud

In Memeo's case, version 2.0 of its software continues to offer drag-and-drop uploads (even folders!) and automatic synchronization. But it goes further with a combination of features that make using its so-called GDrive a more viable option. For example, you can save files from your desktop-based applications like Microsoft Office directly to Google Docs via GDrive, and you can open GDrive-hosted files with its associated native desktop program. In other words, it blurs the line between the cloud and the desktop, just as Google's mythical GDrive would have supposedly done. And for that reason, we don't at all begrudge Memeo the name "theft."

Memeo Connect's other new features include the ability to select multiple files at once for deletion (from the cloud), filter files by type or category, download all Google Docs with a click, view folders shared with you via Google Docs and more.

And let's not forget one of the most exciting new features: full text search for documents, another benefit of the in-depth collaboration between Memeo and Google when building this new version of Connect. To truly transition to cloud-hosted files, this feature is considered a must-have for many users.

For Business Users Only?

Memeo Connect is more business-focused than it is a consumer tool. It's not available as a "freemium" offering, as some would expect. Surprisingly, that's not Memeo's decision, but rather Google's. Google restricts its API usage for these types of synchronization services so that they only work with those who have business-level accounts.

As far as pricing goes, for Google Premier users, it's $9 a year per user and for non-Premier users, it's $59 a year per user, which includes a new Google Apps Premier Account in addition to the sync service.

Memeo Connect 2.0 is available for free evaluation from here. Both Mac and PC versions are available.

According to Google's blog post about the beta release, the sync feature has to first be activated on each of your computers where Google Chrome is used. To do this, you'll need to download the beta build of the browser available here. Once installed, click the "wrench" menu (yes, the one with the wrench icon) in Google Chrome and select "Synchronize my bookmarks" from the menu that appears. Sign into your Google account in the dialog box that pops up. If you've already set up Sync on another computer, you'll then be prompted to confirm that your different sets of bookmarks should be merged together. In that case, click "Merge and Sync" to complete the process. Finally, click "OK" when you've finished.

Not only does this feature sync your bookmarks, it also creates a copy of your bookmarks file on Google Docs in a new folder called "Google Chrome." (Wonder what else will go in that folder in the future?)

What's in Store for Sync

For now, the Sync feature is only synchronizing browser bookmarks, but the framework behind Sync is ultimately designed to handle the synchronization of other kinds of browser data as well. As to what sort of data that could be, Google can't provide any official confirmation just yet. However, they did say that you could imagine that "this type of infrastructure could be extended to other types of user data such as passwords" in the future. We'll speculate that it will eventually include those passwords, your browser history, and whatever favorite websites appear as thumbnails on the New Tab page. After all, if Mozilla's Weave Sync prototype can handle those sorts of tasks already, there's no reason to believe that Google couldn't do the same.

Because the new Sync feature uses an XMPP connection to synchronize the changes, changes made on one computer are synchronized immediately to another. Not just quickly, mind you, but immediately. This is possible because XMPP is what's known as a "real-time" communication protocol - the same one that powers Google Talk, the company's IM service.

The use of this sort of technology hints at how Google plans to make their Chrome web browser the core of their upcoming netbook operating system, Google Chrome OS. The new OS will run web applications "in the cloud," a radical change from current OS offerings where many applications are still installed on the computer's hard drive itself. With Chrome (the browser's) ability to synchronize data in real-time between computers, it's easy to see how a cloud OS could operate. It wouldn't matter which machine you used, your data would be available, stored in the cloud, synchronized, and all accessible upon login to your Google account. That prospect is either amazing or terrifying depending on your trust level when it comes to Google. Perhaps it's even both. 

Chrome Gets Faster, Too

While Bookmark Sync is the most interesting feature to debut in the new beta, there are some notable speed improvements to mention, too. The latest build improves performance by 30% since the current stable release of Chrome and by 400% since the very first stable release, as measured by Mozilla's Dromeao DOM Core Tests. 

As noted earlier, speed was a major factor in Firefox's 3.6 beta 1, released just this Friday. Both companies are going head-to-head when it comes to browser speed, JavaScript performance and startup times, but no official speed tests have been done yet to compare the two new beta releases.

To download the latest build of Google Chrome beta, head over to the Chrome beta site here. The official beta requires Windows XP SP2 or higher.

Just last week, MySpace also announced that its users can now sync their updates with Microsoft's Live profiles. For now, the new two-way sync feature only works with Twitter, though the company notes that it will soon support other networks as well.

AOL also just announced two-way syncing with Twitter when it launched its AIM Lifestream service last week.  Overall, these services aren't very earth-shattering, but it is good to see that MySpace continues to open up and create more links with other services.

It's also becoming increasingly clear that Twitter is now the de facto clearinghouse for status updates. Pretty much every new service that features status updates already pushes updates to Twitter and now most of the older services are also (slowly) coming on board.

With Weave, Mozilla Labs currently offers a very similar feature, though Weave hasn't made it into the default install of Firefox yet. In the past, Google also offered a synchronization plugin for Firefox, but the company discontinued this service in December 2008.

Link to Chrome OS?

Of course, we can't help but wonder if this work isn't also being done in preparation for the upcoming release of the Google Chrome OS. A lot of the work to get Chrome to sync between different instances is being done at the backend. If Google could get its netbook OS to seamlessly sync with applications on the desktop, then that would be yet another selling point for the Chrome OS.

Privacy?

Chances are that you are already storing your search history on Google's servers. With Chrome's synchronization feature, however, you would also store a complete record of all of your comings and going on other parts of the Internet on Google's servers. Mozilla Weave encrypts your data before it is synced with Mozilla's servers. In today's announcement, the Chrome team did not talk about encryption, though we would be surprised if Google didn't implement client-side encryption as well.

For some users, though, giving even more information to Google - even if it is encrypted - may turn out to be a deal breaker.

Get the Dev Channel Release (if you dare)

For now, only users who have installed Chrome's developer version and are subscribed to the Dev channel will see these new features. The Chrome Dev channel is the most frequently updated, cutting-edge version of Chrome, but these version are also far less stable than those in the more mainstream Beta and Stable channels. If you would like to switch to the Dev channel, instructions for installing this version of Chrome can be found here.

According to a post on Apple's website, the company is now claiming - for the record - that they will not guarantee other devices will sync with the iTunes software nor will they support those devices.

Here's how the post reads:

Apple designs the hardware and software to provide seamless integration of the iPhone and iPod with iTunes, the iTunes Store, and tens of thousands of apps on the App Store. Apple is aware that some third-parties claim that their digital media players are able to sync with Apple software. However, Apple does not provide support for, or test for compatibility with, non-Apple digital media players and, because software changes over time, newer versions of Apple's iTunes software may no longer provide syncing functionality with non-Apple digital media players.

That sounds like a definite slap in the face to the Pre who may soon see one of their main selling points disappear with a simple update to the iTunes software.

Still, Apple has to be careful not to implement the update in a such way that makes it appear that they've done so just to break the Pre's syncing ability...that would reek of anti-competitiveness and could get them in trouble with the U.S. Department of Justice. However, we know Apple is filled with enough smart people that they could surely think of a way to break it without making it look like they broke it on purpose . The question is, will they really do something that under-handed and sneaky? Or do they just want to create a climate of fear by implying that you can't trust the Pre to always work?

Either way, it doesn't look like good news for Palm.

Who came out on top? Why Funambol, of course. That alone probably makes you wonder if any of the data from the study is worthwhile or if it's all been skewed in their favor. But parsing through their report, there are some interesting tidbits about the state of mobile sync.

Each solution in the study was compared across ten attributes: cost, supported devices, synced data, web portal, wireless desktop integration, social network sync, usability and performance, global readiness, open source and standards, and brandability and customizability for 3rd parties.

Cost of Sync

When it comes to cost, 75% of the mobile sync solutions out there are free. Note that this report does not include specialized mobile applications such as those found in the App Store. Blackberry Internet Service (BIS) was the most expensive at $20 per month and Apple's MobileMe was second most expensive at $99 per year.

What to Sync?

An important consideration when choosing a sync service is finding one that syncs everything you need. In the study, Funambol found that 41% of the solutions only synced a single item. The solutions that synced four or more data types were the Apple MobileMe, Microsoft MyPhone, Nokia Ovi, Palm Synergy, and Funambol's open source solution.

Along with standard data (contacts, calendar, photos, etc.), a few of the solutions also sync with social networks, most notably Palm Pre's Synergy solution which syncs with Facebook. However, 50% of the solutions studied didn't provide social networking sync - a situation that we think really needs to change.

As the study continues, Funambol rates the solutions on things like "open source and SyncML Basis" and "Branded and Customized Sync for 3rd Parties" - attributes that highlight features specific to their offering, and not necessarily things the average consumer will care about. This skews the overall results in favor of their solution and makes the takeaway from the report somewhat moot. Still, before they got all self-promotional, there was a bit of interesting data to discover, as we've highlighted above.

In the end, though, none of the sync services on the market are really perfect solutions as of now, something that we mentioned before when lamenting the terrible contact management solutions out there today. We're still waiting for something to blow us away here and it just hasn't happened yet.

While it's great to see a mobile device include out-of-box functionality for contact import from webmail and social networking sites, there's still a major problem with this type of syncing: no filters. You see, most people don't want their entire contact list from any online resource dumped into their phone. The reason is simple - we just don't phone all our online friends.

Think about who you've friended on Facebook. Unless you've been extremely selective, I can guarantee you that you have more than a small handful of what can only be called casual, online acquaintances. Maybe they're people you know from around the 'net or maybe they're those old high school friends who wanted to catch up. Either way, what they're not is people who you need on speed dial.

Now think about who's in your Gmail address book. If you've been with Gmail since the beta days (oh wait, they're still in beta...ok...the private beta days), your address book there is probably over-crowded with hundreds if not thousands of random email addresses belonging to people you don't know, bots, and auto-responders. Hardly the kind of data you'd want in your phone.

And yet, on the Pre, all this data is being dumped into your device without any sort of advanced filtering going on. That would almost be OK if the phone also offered some sort of "favoriting" or filtering mechanism after the data is loaded so you could see different views of your contacts, but instead, they're just all there. Instead of a simple, compact list where it's easy to find your actual contacts, you have no choice but to start typing to find someone by name. There's simply too much data for scrolling to be worthwhile.

All-or-Nothing is Good for Nothing. Why Can't We Sync Lists?

This problem isn't limited to the Pre alone. Android pulls in all your Gmail contacts and some of the contact apps for iPhone which sync with Facebook like MyPhone+ for Facebook (iTunes URL) just dump your friend list data in its entirety, too.

This is a shame, especially considering that both Google and Facebook as well as many other webmail services offer ways to create contact lists or, as they're called in Facebook "friend lists." But why isn't there a program that lets you pick and choose which lists come into your phone? Why is it all-or-nothing?

Call, Email, or Text...What about Tweet, Wall Post, and Share?

But too much of a good thing isn't the only problem with contact management programs today. There's also the fact that they only let you communicate in traditional ways: call, text message, or email. Why don't contact managers offer features that let you send a tweet to your friend? Or post something to their Facebook wall? These new types of public communication are just as important as the old ones.

Phone calls and texts are great for private, personal chats. Emails are better for sharing info - especially attachments - and communicating with business colleagues who don't need to be bothered with small talk. But Twitter and Facebook let you share something with a friend...and also with a network. On Twitter, that's a more public type of sharing (if it's an "@" reply, that is) and on Facebook, it's somewhat public, but with a closer network of friends.

Then there's the issue of multimedia sharing. Why can't I post a video recorded with my phone to YouTube at the same time I send it to my friend's phone, or do the same for a photo and post it to flickr, MMS, or another device?

The closest application we've seen to offer this sort of functionality is Asurion's social address book, which debuted at DEMO 09. Unfortunately though, the app is limited to Android phones and is still in private beta.

Developers: Enough with the Twitter Apps, Build this Instead

With all the growth taking place in social networking sites over the past few years, the ability to incorporate the social element more deeply into our phone's contact list is an area that is crying out - perhaps even screaming - for innovation. But instead of building something useful like this, so many of today's developers seem too content to create yet another Twitter application,or even clones of ones that already exist!

Why isn't someone working on an address book application that will blow Palm Pre's "Synergy" out-of-the-water? We want to see something that makes the Pre look behind the times. We want to see something powerful and, oh, while you're at it...cross-platform too. (Cough, iPhone first please, cough). If someone out there is building this app, please let us know. We'd be the first to sing its praises.

Image credit Palm Pre: forum member retroremakes