Facebook is thriving in part because it embraced the virtual goods models, where third-party companies such as
PlaySpan supply the currency system so that goods in the game can be inventoried, tracked, exchanged, sold or cashed in. As this model kicked into high gear this year, it replaced the pure ad-driven models of the web or the try-before-you-buy model of casual downloadable games. On Facebook, virtual goods could generate $500 million in revenues this year, according to estimates in our past stories.