Remember, though, that nobody thought search was monetizable when Google dominated it. They didn't have a business model until almost 2 years in: at the time, the fad was to turn search engines into "portals" and cash in through banner advertising on the home page.

FaceBook also has the advantage of being locally-based: ads can be targetted very specifically to people within range of local businesses. People don't really search for restaurants within walking distance, and even if they did, Google doesn't know where they're located. Facebook does, however, and can display ads for local businesses that the user might not be looking for now but might want to visit later.