Facebook is the [social graph] market leader for sure. But its not winner takes all because its just too big of a category for innovation & creativity. Right now my social network for music isn’t on facebook (instead it’s on hypemachine and tumblr). My photo social net is on tumblr and flickr. My social net for television is Boxee. My information social net is Twitter. Foursquare and Twitter are my social net for places & events. The list goes on.