What do you think about a site allows users to attach identity to a bitcoin address? It allows users to trade anonymity for trust. One could verify different pieces of identity such as email, phone, facebook account, physical address, id, etc... and earn a score for what they verify. The information would be kept secret while the score could be looked up by anyone. A buyer could see that "oh, this btc address has verified their home address with this third party, so I can find out where he or she lives should I get ripped off." Would you use this service to look up btc addresses? Or use it to verify your address if it allowed you access to better rates or trusted merchants? What about if you earned some BTC for each point of identity attached?
I was just thinking of something like this myself. I think it would be a great idea but you're right, exactly how much information to release and who to would be the big issue. Maybe the receiving user would choose to allow their information to be divulged to the sending user before the transfer by use of the UI.