The question now is: should you use it? Or should you stick with your favorite check-in application, like Foursquare or Gowalla?

Latitude is Google's own take on friend-tracking location-based services. Like Foursquare, you can use Latitude to see where your friends are, but the similarity ends there. Latitude is a completely different animal than your typical check-in app.

On check-in applications like Foursquare, Gowalla, Loopt, Brightkite and others, you check in to a physical venue through a very manual process. To check in, you launch an app on your smartphone, it locates you via GPS and returns a list of places. You then select the location where you are from the list provided and the app will check you in to that place. It may also dole out a virtual reward of some kind for doing so, including things like points, a stamp or badge or, in the case of Foursquare, the honorary title of Mayor if you've checked in to that venue more than any other user. Sometimes, a coupon or discount is provided by the merchant to those who participate by checking in, too. However, outside of urban tech hotspots like New York and San Francisco, this is still a decidedly hit-or-miss operation.

Latitude, on the other hand, is a real-time tracking service. There aren't badges and coupons here, there is only a pushpin on a map, indicating your location. For users of Google's Android smartphones, tracking your location as you move around town is a built in feature, assuming you've opted in to the service. No dedicated app is needed - it works within Google Maps. However, on iPhone, background location-tracking of this nature requires a native app.

Up until now, I've been using Latitudie for this purpose on iPhone, a third-party application that shares my location with my Latitude friends (err, friend - more on that later). Unfortunately, a recent update has left the app non-functional - it always crashes now. An official Google app will be welcome, to say the least.

Is Latitude Right For You?

But the big question you need to answer now, as the service is poised to become a hundred times more useful thanks to its new, true cross-platform nature is this: should you use it?

Latitude has three privacy settings: detect your location (automatic), set your location (manual) or hide your location. Frankly, the only setting that makes the service worth using is its automatic detection functionality. That alone delivers a huge benefit over Latitude competitors like Foursquare, for example, which requires additional third-party applications like Mayor Maker or Future Checkin to perform automatic check-ins on your behalf.

Of course, you could manually set your location in Latitude - and I'm sure some of you do - but if you're bothering to do all that, why not use a service where you're liable to get an occasional discount or coupon instead? Or, alternately, a dedicated app for private location-sharing like Glympse? (More on that here.)

Over-Friending is a Bad Idea on Latitude

Although Latitude's background tracking is great to have, this major benefit is also the service's biggest privacy concern, too. Automatically sharing your location, in real-time, with all your friends? They had better be good, good friends. In other words, think carefully before accepting friend requests from "that guy you know online." As for me, I only use Latitude with family. I use check-in apps with a wider group of friends.

Some may dismiss this as being overly paranoid, but I think it's just paranoid enough. As a technology enthusiast, I'm happy to embrace location-based services to some extent, but I draw the line at allowing a wide group of "friends" - the same online group of early adopters that follows each other around from service to service - to track my physical location in real-time, plotted on a map. Maybe it's partially because I'm a woman that I feel this way. Or maybe it's because enough of my friends and family have been victims of violence for me to not casually disregard my own privacy and safety, but ultimately the main reason is this: the only person who really needs to know where I am at any given moment (and vice versa) is the one I'm married to. (That metaphor would extend to the rest of my family, too, but the little one is still in diapers - no smartphone yet.) Meanwhile, if my friends want to meet up for coffee, they're welcome to call, email, Facebook or text.

That's an opinion of course. You may feel differently, and that's fine. The trick is figuring out how much location transparency you're comfortable with before signing up for services like this and friending dozens of folks. At least Google is kind enough to send regular emails reminding you that you're sharing your location on Latitude, in case you've forgotten. That effort shows that even Google takes your location-sharing seriously; you should certainly do the same.

Fifteen-month-old Foursquare is adding 100,000 new users every week, and Facebook has made it clear that location is a feature it is preparing to offer soon. What's the motivation for users to register where they are in the offline world online? We asked some users of these services and found that they had varied and interesting answers.

Of course, location services vary widely in nature. Nick Bicanic's startup EchoEcho, for example, is a very discreet service for letting one friend know where you are at a time, emphasizing extreme ease of use. OK Magazine's new celebrity-stalking location app might represent the other end of the spectrum.

Most people who shared their experiences with us were using one of the big social location apps: Foursquare, Gowalla, Google Latitude or BrightKite. Real-world businesses are starting to make interesting use of these services. (Here's one list of 21 different examples.)

The types of places users check into are somewhat diverse, too, though the stereotype of Foursquare users as youthful bar-hoppers is largely confirmed by the numbers. According to a data visualization by the independent group BitsyBot Labs, bar check-ins on the service beat out check-ins at places of education and parks almost all last week. Bars were about equal with the arts and entertainment category. Food and shopping reign supreme, but on most days travel tops drinking, too.

Those numbers tell you something about aggregate activities, but why do individuals participate in this in the first place? It's emotional, and it's different for different people. Will location apps become far more popular once mobile coupons become ubiquitous, and people can save money by using such services? Maybe, but there are clearly other types of incentives already available.

Serendipity and Connection

San Francisco entrepreneur Pat Diven uses location-based social networks for probably the best-known reason, in the types of circumstances you might expect. He's checked in on Foursquare more than 400 times, including at the bloggers' event WordCamp, more than three times at an Apple store, and at more than 20 different pizza places. His Plancast account, where he records not where he is, but where he will be, indicates that he's the kind of guy who likes both big tech conferences, as well as things like camping in Big Sur and beer and music parties in the countryside.

"I use location for chance meetups with people I know in the city," he said last Friday afternoon via a Twitter client on his phone. "It's worked a few times." Diven also raised a common concern, articulated as a sophisticated social network user might: "Hoping for more granular control soon!" He's a good example of an active person who both exposes a lot of their activity publicly and has entirely private accounts on other services.

Diven exposes enough, though, that I was able to see a lot of information about what he likes to do just by looking around online - I didn't speak to him for this article beyond trading a single tweet. He's been doing this for long enough (his Twitter account is more than three years old) that he's sure to have decided that a certain amount of public exposure was worth it to him.

Cambridge-based experimental tech CEO Shava Nerad is on the other side of the country and has a different take on the use of location apps to connect with other people. She says for her, it's simple. "I have friends who work in coffee shops and we like to spontaneously clump to co-work," she said by iPhone early Saturday evening. "The rest doesn't matter to me."

Nerad's public Foursquare history is much tamer than many people's - though she did once win a badge for checking in after 3 a.m. on a weeknight, so apparently it's not all about working.

Portland, Ore., consultant Mike M. says he uses location services to track people more than to meet them. His son works in emergency medical services, and Mr. M keeps an eye on him using Google's service Latitude, "hoping he stays safe." (I called him Mr. M. just because I don't want to see his kid get in trouble.)

Location apps for tracking people around medical matters? That kind of thing makes many people take pause. Some of the same types of tracking technology are being incorporated into medicine and are in many cases causing a substantial reconsideration of patient privacy.

In the consumer world, it's different. Last week I showed my dental hygienist who else was checked in to the dentist's office on Foursquare at the same time I was, and her first reaction was concern about HIPAA (the federal Health Insurance Portability and Accountability Act, which regulates the security and privacy of health-related data). She decided no one could stop the patients themselves from exposing their own location; she just couldn't confirm to me whether or not she actually knew who those people were.

Much more straightforward, in the people-connection department, was my wife's comment left on Facebook last week when she got home and I was gone. I had checked into a coffee shop and pushed the update from Foursquare to Facebook, and she commented "there you are! I was wondering where you went."

Be it for chance or as an exercise in caution, the uses of location services for tracking other people are just beginning to become clear.

For the Win

Many of the popular location-based social networks present themselves as games. They give points to users for going to new or multiple places, then tally the points up against the user's friends. Does that really motivate people to check in? Does it motivate people to go to more or different places?

Apparently, it does. New York City author, social media consultant and mom Tamar Weinberg says, "people disagree with the concept of badges, but I think it's fun to chase after new opportunity & status." Hutch Carpenter, almost Weinberg's exact opposite as an enterprise engineering platform executive and a dad in San Francisco, says he sees it that way too. "I second that," he said of Weinberg's explanation.

That ethos of location-based public achievement may go transgenerational, too. Carpenter checked in on Foursquare at Toy Story 3 this Saturday, said it was his 6-year-old son's first trip to a movie theater, and pushed the update to Twitter.

This gameplay isn't necessarily about narcissism. Virginia-based developer Alex Stone, who says he's made several friends because of Foursquare, says of competing service Gowalla that "[its] quest for items and trip pins has led me to discover some really cool spots in my own small town."

As a Personal History

The thing that surprised me most when I asked people why they use location-based social networks is how many of them say they use it primarily to track their own personal history. It's a lazy diary, people say. I thought, naively, that I was the only one who felt that way.

Some people say they use it to help with their expense tracking on business travels.

Buffalo, NY, Web developer Adrian Roselli told me Friday that he started using BrightKite "so I could post photos in real-time while traveling and associating each with locations on maps." He says he publishes the RSS feed of his check-in history to a map he can view later, to trace his route. That's really geeky, but according to his check-ins, Roselli spent Friday night having dessert with a woman and Saturday morning on a charity bike ride. So apparently, you can push a check-in feed to a map and still maintain some connection to the kinds of things that normal people do. Several people told me they are doing technical things like that with their check-in histories for self-awareness.

When I went to New York with my wife earlier this month, she grew very tired of me pulling out my phone to check in everywhere we went. But once we got home, she admitted it was nice to be able to scroll back through the updates to Facebook I published and remember all the places we had been.

Or, as Palo Alto's Spencer Schoeben told me this weekend, "I love looking back at my check-in history and remembering the awesome things I've done." Schoeben is the 16-year-old founder of one startup company and CEO of another, so he's recording a busy young man's history with those check-ins.

Schoeben has reason to be proud of his accomplishments - and maybe we all do. The one rationale for checking in no one I talked to claimed for themselves - but that one very perceptive person quietly told me was probably more common than not - was showing off. "To non-explicitly brag about your coolness and/or importance, based on where you eat, drink, work, and travel." That makes sense to me. Heck, I'll own it myself, to some degree.

Did I feel a little cool when I checked in at Manhattan's underground Ping-Pong venue and bar called SPiN New York and wrote "Crazy place, ping pong balls flying everywhere, hitting me while I drink beer and blog"? Yeah, I did. Was I aware of what I was doing the next weekend when I checked into two mid-century modern furniture stores in a row? Yes, throw me to the type of piranhas that eat people like me! I was aware of what I was doing.

There are clearly many different reasons people use location-based social networks. Many of us use them for several different reasons ourselves, at different times.

There are, of course, other sides of the story, ranging from the very serious to the somewhat serious. Dan Tynan wrote this weekend at IT World about why you should consider not participating in these kinds of services. Tynan writes a blog called Thank You For Not Sharing, which says it includes "a fair amount of whining." (It's really quite funny.)

Presuming you're fully informed (though that's another matter), then whether these services are for you comes down largely to your circumstances and your attitude. They aren't for everyone. But they are a good experience for some people, as the stories above illustrate. If you've ever wondered why on earth someone would use a service like this - that's why.

After the privacy concerns raised over the hasty rollout of Buzz, Google is being very careful to integrate privacy controls into the Latitude API. Users will have to grant access for the applications they chose to use and will be able to control whether the apps can see their best available location or a city level location.

With its Latitude API, Google is in a way providing a free and open alternative to SimpleGeo, which provides a similar back-end location infrastructure but charges applications with over 1 million users. The ability for app developers to easily leverage Google's network of Latitude users for free could lead to the creation of some truly unique location-aware applications.

This is an important subject for those companies looking to enter into the geo-locational space. Groups that encrypt their data are taking pains to reduce the threat of identity theft, illegal surveillance or for data to be subpoenaed by a court. These companies will be rewarded with customer loyalty when the unfortunate time comes for one or all three of the above scenarios.

Those critical of encryption might suggest that law-abiding citizens have nothing to hide, but that simply isn't true. What if you're in alcoholics anonymous? Or you've simply spent the night at a person's house? And honestly, do you really want your running club to see how often you eat at Arby's? Encryption allows us to ping our friends while maintaining an air of mystique, and at the end of the day, the companies that care about their customers, keep them.

For the Google public badge, users can choose if they want the widget to show their location at a city-level only, or if they want to allow it to show their location more precisely. Given the public nature of the badge, this will surely raise some security concerns, especially when users choose to update their Latitude data automatically.

The Google Talk widget only uses the name of the city the user is currently staying in to update their status.

Google stresses that it takes its users privacy very seriously, but there can be no doubt that privacy concerns are currently limiting the mainstream appeal of many of these applications.

Google is clearly taking a very serious look at location aware services and according to today's blog post, the company plans to introduce more applications that can make use of one's Latitude data in the near future. Google is also soliciting new ideas from its users here.

Bliin

Bliin is a Dutch service that combines the location sharing of Google Latitude with the journey recording of Nokia's viNe application (our coverage). With Bliin, you can explore the world around you, zooming in and out on the map while viewing geo-tagged photos, the last recorded locations of other Bliin users, and even the live movements of anyone sharing their journeys on the network. So why isn't Bliin catching on? Blogger Martin Bryant theorizes it could be because the network doesn't integrate with your address book the way viNe or Latitude does. It's also a much smaller European company without the financial clout of either Google or Nokia.

Toaí

Toaí (Portuguese for "I'm Around") is actually a new social network which, at first, appears to be just like any other: you sign up, create a profile, etc. However, Toaí also asks you for your mobile phone number which it uses to text you with music, art, and stores that are near where you are. The recommendations it sends are based on you and your friends' favorites. It also lets you know when your Toaí friends are nearby. Toaí is a great example of how a social network can add in location-based features to take networking beyond the virtual world and into the "real" world. Unfortunately, there is no English-based version of Toaí yet.

Parallel Kingdom

Who cares what your friends are doing when there are dragons to slay, enemies to fight, and weapons to upgrade? The new RPG (role-playing game) Parallel Kingdom for Android and iPhone uses location-based networking to let you see other nearby players on a Google map. Also, when finding monsters to battle, you have to physically move to a new location to do so. The end result is a mashup of traditional gaming and geocaching. (U.S. Only)

Radar

Outside.in's new iPhone application Radar (not to be confused with the photo-sharing iPhone app also called Radar) delivers location-based content including news, blog posts, and tweets to your iPhone. Once installed, the app will geo-locate you upon being launched to deliver the news within 1000 feet of where you are standing, from your neighborhood, or from the entire city. You can also load up Radar with profiles for various locales, including your home, office, and more. Shake the app to switch from the news listings to the map view. (U.S. only)

More Noise to Signal

Knowing where people are is great. Being able to get ahold of them is even better. That's why Latitude also lets you interact with them by providing access to SMS and IM or allowing you to call them.

It's All About the Data

While many of us have grown used to providing details on our travels by updating location-aware apps like Brightkite or checking in with sites like Dopplr, those journeys have always been loosely affiliated with the rest of our habits - through a lifestream, at best. Today, with Google gathering this information, it changes the picture entirely.

For millions of users, Google already knows how they search, what they click, what they buy, who they know, how they communicate, and where they go on the Web. Location enables them to add another critical data point - where they are when they're performing any of those actions. So if you think Google has too much information about you already, you've got another think coming.

Long story short, Latitude adds a whole new level of complexity to Google's understanding of you and your habits. And while we'll no doubt derive some very interesting benefits from sharing that information, we should hold no illusions about the value of that data to Google and its efforts to run a profitable business.

But, in Google's defense, they've also worked to ensure you have a way to opt out of the service and maintain complete control over your privacy. Katherine Boehret of The Wall Street Journal, who has had the opportunity to test drive Latitude for the past week, also gives a nod to those opt-out features:

"Usability issues aside, location-based services like Latitude can be just plain creepy, especially when a Big Brother like Google is tracking your whereabouts. So Google incorporated easy-to-change privacy settings so that locations can be automatically detected, manually entered or completely hidden from other people. Or people can sign out of Latitude altogether."

Do No Evil, Please

It was only a matter of time before Google entered this market, and no doubt millions of people will soon be flooding the service with their up-to-the-minute location details. With the combination of Google Maps, Google Latitude, Google Friend Connect, and Android, it's not very difficult to begin daydreaming about the potential for this service.

But it's also a leap of faith as a user, entrusting Google with yet another piece of data that helps them figure out the puzzle of understanding you - and how and where you're likely to perform actions that put money in Google's pocket.

It will be interesting to see where Google goes with this one - and interesting to see where you're going, now that we can look over your shoulder.

Update: See our follow-up analysis Did Google Just Kill All the Other Mobile Social Networks?