I think Facebook really could make a crap-ton in any number of ways, just from all the user data they have available for mining. Advertisers would (and already do) pay through the nose for that. I think ad revenue is generally an awful money source for a web app, but Facebook is big and addictive enough to command some crazy rates.

And that makes me scratch my head when they talk about "building the userbase" and "not focusing on revenue yet" Maybe I'm just short sighted, but I think it's time for FB to start cashing in. Just like anything else, it's best to launch your revenue model early and iterate, rather than waiting until the timing is perfect.