Excepts: As of late January 2008, more than half-a-million Facebook users play Scrabulous daily, with four times that number having added the application to their Facebook profiles. Because third-party developers can keep all the revenue they generate, the Agarwallas are currently pulling in about $25,000 a month from advertising, according to Jayant, resulting in a "decent profit" after expenses like hosting, labor and server costs.

"I know so many venture capitalists and CEOs who play Scrabulous. It's a new form of golf. Maybe you don't have time to play nine holes, but you can socially interact and challenge one another via Scrabulous," says Rumford, CEO of the Solana Beach, Calif.-based Gravitational Media and publisher of Facereviews.com, a review site for Facebook applications.

"The main selling feature of Scrabulous for me is the fact I can play it within Facebook. If it was on an external site, I would have to search for my friends all over again, and I don't think that would work, and I don't think people would sign up for it."

A few major brands have made it big on Facebook, like Red Bull, the energy drink produced by Austria-based Red Bull GmbH, whose Facebook application "Roshambull" offers an online version of the classic children's game "Rock-Scissors-Paper."

Online dating is another area where big players are lagging. Like the Agarwalla brothers before the f8 launch, Cliff Lerner ran a website, in his case called Iamfreetonight.com, an online dating site owned by the Manhattan-based eTwine Holdings. After the Zuckerberg announcement in May, Lerner recalls, "We decided to stop working on Iamfreetonight.com for a couple of weeks in order to write a dating application for Facebook." The result was an application called "Meet New People." "In no time we had more users on the app than we had on the website. And we didn't spend a dime on advertising the app -- it was all viral."