MySpace, Friendster, Orkut, Hi5, Bebo. I'm sure there are others that I'm missing.
They have played pretty hard in the virtual currency area too (although if anyone really thought they'd be able to build a business in that area on Facebook then I've got a bridge to sell you)
I take it you didn't see Chris Hecker's GDC talk? It was all about the real world gaining these MMO like rewards. It was fascinating and horrifying at the same time, but I'm hoping it will never be a reality.