It is worth noting that Facebook maintains "ghost" profiles for people who aren't members, but of whom they are aware. I'm having trouble finding a reference, b

It is worth noting that Facebook maintains "ghost" profiles for people who aren't members, but of whom they are aware. I'm having trouble finding a reference, but I remember it came out that when your friends ("friends") give Facebook their email contacts so that they can locate other people using their service, Facebook remembers contacts which do not yet hold accounts. I speculate this information wouldn't be valuable if they didn't attempt to infer that particular posts mentioned these non-member profiles.