Earlier quoted context omitted.
Why is it inevitable? They already run an ad network and their revenue's are nowhere near, for example, Google's. How else can they monetize this data?
They've barely scratched the surface. And it's not just an ad network... - virtual currency - daily deals - search integrated directly into the experience and that's just off the top of my head
I'm not saying Facebook cannot be wildly profitable, I just don't think it'll come close to the top 10 (what I'd consider to be "the most profitable companies in the world").