The first thing to realize is that Facebook is in fact a bank. It doesn’t have a charter and its not regulated*, but it accepts deposits from consumers, and provides means for payment using those deposits. In my book, thats pretty darn close to being a bank.
Facebook Credits are really deposits
This becomes clear when you realize that you have to give Facebook money in exchange for those virtual Credits it gives you. You can use Credits for payments of course. But till you actually do that, Facebook is in effect holding that money for you. In other words your money is deposited at Facebook, and you trust Facebook to hold that money for you safely till you decide to spend it.
More details about this provocative article can be found at: http://shamirkarkal.blogspot.com.au/2012/03/fastest-growing-bank-in-us-is-facebook.html