Facebook generates 85% of it's $3.7 billion annual revenue from advertising. But the jury is still out on its usefulness as an adviertising medium.
Yes you get access to 900 million people. Yes you can mico-target. And in the days of traditional interuption-based advertsing, that would all but guarantee success. But the social web is creating its own rules of engagement which is leaving many traditional advertisers like GM scratching their heads over why Facebook advertising doesn't work for them.