When Facebook founder Mark Zuckerberg announced in May that his company would open its platform to third-party developers, a tingle ran up the spine of every ambitious programmer and Google-struck entrepreneur in Silicon Valley.

But while widgets make it fun to show that you've been to 167 cities or that your pimp name is Luscious Dynamite, the really heart-palpitating question remains: If Facebook is not selling ads on these widgets, who's going to make the money?

In the latest internet land grab, at least eight companies have launched advertising networks for Facebook widgets. The players include Lookery, fbExchange, Cubics, Social Media and the latest addition, Appfuel. Several content distributors, including RockYou and Slide, as well as video-solution provider VideoEgg, have also gotten into the ad game. But the specter looms: Facebook giveth, Facebook can taketh away.