I read in Rolling Stone that Facebook is worth as much as GM (as in General Motors). Mark Zuckerberg, the Founder and CEO is only 24.
All is not sweetness and light, though. Currently, several people who came up with the idea at about the same time he developed it are suing him (for zillions, I assume). And I must say that the R. Stone article painted a picture of him being a pretty nasty guy.