It is an interesting concept, and when you think about it, it's not really SO different from what Fico already does. It gathers a bunch of information about you and assigns you a risk score based on how other people with the same information behaved. That said, I would think this is even more open to manipulation and probably less reliable than other factors that are more closely related to your finances.
In cultures where financial information is considered private, and many people (even some of us on these forums, I would imagine) hide - or choose to not disclose - the actual state of their finances from their friends and much of their family, it seems that your friendships might not be a great predictor. And can you imagine the buying and selling of Facebook friendships to help you get a loan?