What other product do you know of that every business uses, and every person uses everyday.This potential revenue stream for FB is endless.That's it right there, case closed; check mate.Google was nothing 5 years ago. They attracted people, and then matrix styled products at them. (android , ad space)Facebook will do the same.
Google stole market share away from MSFT. If facebook can do that, they will be like google, but they are just social media.