An infographic from Single Grain, has some interesting statistics about Facebook gaming.
All Facebook notes right off the bat, that there are currently more Farmville players than actual farmers in the U.S. and one out of every five people plays the game.
* 20% of the Nation has played a game on a social network, and of that 20%, 35% have never played any other kind of video game.
* 55% of social gamers are women, and of those 55%, 78% earn virtual currency via promotions.
* 90% of Zynga's revenue comes from virtual goods.
* The teddy bear purchases in Mafia Wars raisted more than $100,000 for Coalition for the Cure in March 2010.
* While online, the average American spends more time on Facebook than Google, Yahoo!, YouTube, Microsoft, Wikipedia, and Amazon combined.