Bitten by a zombie lately? Had a plate of spaghetti thrown at you? Figured out your porn-star name? No? Then you obviously haven't been one of the 30 million Facebook users who've downloaded 80 million such applications on the social-networking Web site since May.

As frivolous as these software functions appear, they've become a cornerstone of the Internet firm's success and have attracted huge buzz -- and not just among the geeks of Silicon Valley. Last week, Barry Diller's Expedia, the $8 billion online travel agency, paid $3 million to acquire one of them. "Where I've Been," developed by a Facebook denizen, allows users to display a map detailing all the places they've visited.

Expedia's purchase, which will be folded into its TripAdvisor unit, isn't the first deal for a Facebook application, but it's certainly the largest. It values each of Where I've Been's 2.4 million adherents at $1.30 a pop. Those aren't big numbers. But it gives a glimpse of the potential value to be mined on Facebook, which has approved 3,000 applications since opening the Web site to developers.

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