Facebook just raised $500 millions. The social network is supposed to be worth $50 billions! Quite a lot, since their annual revenue is about $2 billions.
Facebook knows a lot about their users (almost 600 millions!). Facebook knows your gender, your age, your friends and your activities. Thanks to Facebook Connect, Facebook also knows most of sites you've visited.
If used smartly, Facebook can use this data to
serve relevant ads and become the king of targeting. Even better than Google and with a much wider range than
Criteo. This is the way ads will be sold in the future. Prices will be determined depending on the web surfers, not depending on the web site hosting the ad (see the article: "
Give value to the audience").
The question is: why does Facebook need money? Because they want to build a wider ad network. Something similar to Google AdSense, but dedicated to display advertising. The money will be used to develop this network.