My belief is that with straight up direct ad sales and limited targeting ads, MySpace cleared $1B this year. That's the potential upper limit of how much Facebook can make with just straight up ad sales.
But having a much more complete understanding of relationships, Facebook wants to find something more effective and profitable than AdSense. That's what Mark Zuckerberg really pitched to everyone that has invested into Facebook: his team's ability to reinvent online advertising.
The products they have so far -- Beacon, Social Ads -- are kind of lame but Facebook Connect is getting pretty big and they have quite a lot of money and time to work on it.
But all this doesn't matter. Facebook isn't profitable! And somehow this affects hackers around the world.