But this isn't just another nine-digit number in the sea of Web business news. Linden Lab, the parent company of Second Life, simply charges fees on financial transactions. Its revenue comes from an entirely user-generated economy built on real estate, virtual goods and services. Yes, there's also a sex industry.

The world uses a currency called Linden dollars, currently trading at about L$ 241.5 / US$ 1.00, and Linden Lab picks up a $0.30 transaction fee when users purchase currency. The company also gets a 5% commission on virtual goods sales on the Second Life Marketplace, and the remaining 95% goes to the user who created the object. Users also pay the company to rent virtual land, representing real-world server space, which can then be developed and bought and sold between users at will. Linden Lab is really merely a bank, providing capital as well as bandwidth, but the health of the Second Life economy is all due to the creativity and effort of its users.

Second Life is a Big Place

As of Q1 2011, the world was around 2,060 square kilometers in size, which would make it the largest city in the continental United States. Users logged 104 million hours in-world last quarter. The average monthly repeat logins, the most meaningful measure of the number of people in Second Life, was about 794,000. It's free to use Second Life, and there are plenty of free clothes and avatar shapes and other goods available. All this economic activity is based on people voluntarily paying for a more immersive experience.

Second Life has been around since 2003, and its usage statistics seem to be more or less stable, neither gaining nor losing significant numbers of users. But the virtual world has reported consistently strong economic growth, and the official numbers are corroborated by independent reports.

Linden Lab hired Rod Humble, a former executive at Electronic Arts, as its CEO late last year, replacing interim CEO and founder Philip Rosedale. The company is currently focusing its development efforts on user experience, providing better and more intuitive interfaces. If the virtual world's economy keeps growing like this, Second Life doesn't have to constantly attract new users into the fold; it can stay focused on making the experience more fulfilling for existing residents.

Second Life is far from the only 3-D virtual world out there (here's a good comparative list), but no other has such spatial or economic magnitude.

But is the Second Life Economy Sustainable?

Update 4:15 p.m.: Wagner James Au, creator of prominent Second Life blog New World Notes, questions whether Second Life can sustain its economic miracle. He cites the $75 million revenue figure, which has been stated in Linden Lab press releases, and he builds a case by breaking down the most important kinds of economic activity in-world. He estimates that the share that falls on the head of each private estate owner is $11,000 per year, which is a hefty cost by any measure.

Au says there are "all kinds of reasons" estate owners wouldn't want to pay that cost forever, and it really doesn't take much to imagine why $11,000 per year in overhead would be a bit steep for a resident of a virtual world. Most importantly, he says, "It's highly unlikely these departing landowners can be replaced." His solution is that Second Life must be made friendlier for mass adoption, and he points to some efforts by Linden Lab to move the service in that direction.

But their profile of the average U.S. gamer varies noticeably from what the Entertainment Software Association found in their 2011 report. The two studies have markedly different measurements of the age and gender breakdown of U.S. gamers.

The PlaySpan and ESA studies had sample sizes of 1,006 and "almost 1,200" respectively. The former was conducted by VGMarket, which concentrates on the video game industry, and the latter by Ipsos MediaCT, a general media, content, and technology research firm. It's not obvious why the two would find such noticeable differences in the average U.S. gamer population. The discrepancy prevents us from drawing any conclusions about spending on virtual currency yet.

Update 8/5, 9:00 a.m.: Commenting on the discrepancy, Michael Gluck, president of VGMarket, says, "In order to qualify for our study, respondents must have purchased at least one virtual good in the last 12 months. This study is all about understanding the average virtual goods buyer, not the average gamer in general. Those who did not purchase virtual goods were excluded from the study." That's not apparent from VGMarket's slides, though. The data in dispute are under the header "US General Gamer Population" (slide 1), and 8% of respondents say they did not purchase virtual goods in the last 12 months (slide 5).

When asked to clarify in light of the seeming contradiction, Gluck repeated his position. PlaySpan's data seem less reliable in light of this conflict.

Before today, you could buy your virtual currency via PayPal, credit card or mobile phone, as well as earn Credits via certain games and apps. But the addition of UltimatePay will help power a variety of additional payment methods, aimed at expanding the global reach of the program.

Making it easier for those outside the U.S. to buy Facebook Credits is a smart move for Facebook. Over 70% of Facebook's users fall into that category, and having a globally-available payment system lowers the barriers for people to buy credits.

A recent New York Times article estimated that the virtual goods market is expected to reach $835 million on Facebook this year. If Facebook and PlaySpan can make it even easier for people to participate in a global Facebook economy, that number is likely to be even higher.

In 1999 Sampo Karjalainen and Aapo Kyrölä started Mobile Disco in their native Finland. The next year, as it grew in popularity, they ginned up what has since become a popular element of online environments, the micro-payment model, and launched Habbo Hotel. Since then 172 million folks have churned out a character, grabbed a room, thrown up decorations, chatted, played games and whatever else it is kids get up to these days.

Of course it hasn't always been roses. Only a year ago, things weren't looking great for Sulake, which had to lay off 40 employees due to a revenue decline of $14 million from the year before. In 2007, the Dutch police arrested a kid for stealing $5,800 worth of make-believe furniture. (No I'm not kidding.)

Here's a little numerical snapshot of our Finnish friends.

• 172 million characters created
• 40 million monthly user hours
• 15 million monthly unique visitors
• 120 million active user-created rooms
• Users from over 150 countries
• 11 languages

Happy birthday, Habbo Hotel. We've sent you a lifetime supply of umlauts. (OK, it's no Kalevala, but it's better than a poke in the eye with a broken Nokia.)

Having only gotten started at the beginning of this year, the team at BOKU has been working at top speed. The company has already received $13 million in financing from Benchmark Capital with participation from Index Ventures and Khosla Ventures as well. They've also acquired two other mobile payment companies, Paymo and Mobillcash, allowing BOKU to start off with a decently-sized customer base and a wide range of participating carriers.

The Virtual Goods Marketplace

BOKU isn't really going up against online payment services like PayPal which requires you to link a bank account or credit card to your account. Instead, not only are they targeting the portion of the online world who don't have bank accounts (but who do have mobile phones), they're also going after an entirely different type of transaction altogether: virtual goods.

Where PayPal has become a popular method to pay for "things" online, BOKU aims to become the standard for paying for "virtual" things - things which include virtual goods in online worlds like Second Life or World of Warcraft as well as in casual games like those found on Facebook, MySpace, and hi5. The company is also working with other game publishers like Gameforge, Aeria Games, and Puzzle Pirates to name a few.

On Facebook alone, there's a virtual marketplace estimated at $500 million in transactions, BOKU's Ron Hirson, Sr. VP of Product Development, tells us. However, the virtual goods market as a whole is worth $8 billion today and continues to grow.

How BOKU Works

The process of paying for these virtual goods via your mobile couldn't be simpler. You just click on the "Pay by Mobile" button provided on the web site, enter in your phone number, and confirm the payment via a text message sent to your phone. The whole process is extremely quick. It's also in many ways a safer way to pay than using your credit card. With a credit card, your number could be stolen and you wouldn't even know until you receive your next statement at the end of the month. However, your phone can't go missing for very long without you becoming aware.

BOKU launches today to serve 1.6 billion customers in 53 countries.

What about the legal issues that torpedo these types of services, time and time again? Just Hear It claims to be paying for "licenses from all the major performing-rights organizations (ASCAP, BMI, SESAC)." Perhaps that proactive stance will save them future litigation.

While Just Hear It does a good job of finding music, the best part about the service is the playback - thanks to the attention to detail on the user interface. Drag and drop makes creating playlists a snap. And the player includes shuffle and repeat buttons - critical features of standard music software that are often strangely absent from Web-based search-and-play services.

That's the good. On the downside, the service currently offers no downloads. So, even if you do find that track you're seeking, you're going to need to be on the Web to play it. And with a Flash-based interface, don't expect to be bookmarking any of your favorite searches.

Just Hear It is currently in private beta. Users can search, play songs, and create playlists, but they will be unable to save those playlists unless they are selected to participate in the beta.

If you're interested in playing some of those hard-to-find tunes you've been seeking, Just Hear It may allow you to do just that.