Let me just say from experience that Facebook ads haven't really generated the same type of return as Google ads. The thing about Google ads is that they are really good at capturing demand that is already out there, like for instance in a niche market where people are looking for a particular product or service (example, search "bike" and get advertisements for bikes of different types, etc.)
What I find is that money spent on Google is money spent on trying to get infront of people "who know what they're looking for." With FB, it's sort of the other way around, where you have all these people you can get infront of, but the demand is more opaque, and you're really searching for it instead of capturing established channels like with Google search terms.
All of this is really just chatter, only FB can know how to monetize FB, because they have the data, they have the information required to make a decision on what to do, and chances are, like with Google (remember in the early days they had no business model), they'll figure it out through just sheer luck or chance. What's amazing is that they have gotten this far already.