Is there a namecoin (or similar) social network? How would it work? I'm looking for information on how Namecoin could create a "Facebook-style" social network and what prior work exists.

I understand that namecoin has fundamental problems and fledgling support, but I'm interested in where this idea has gone in terms of creating a distributed social network.
Well Retroshare somewhat falls into this category. It is not Coin-Based however, rather related to Bittorrent DHT technology und not well documented.

There is also the Bitmessage protocol which uses Coin technology for exchanging mail.

I do not know why you would build such a system as a Coin network, plain BT style DHT is more suitable for this purpose in my opinion. I do not know any good reason why Bitmessage does it this way either. I think it is just overcomplicated and not well thought through. The usecase is just very different from Bitcoin.

I mean, what would be the purpose of the block chain? Prevent double friending?