How does blockchain.info associate a message with an address? I randomly encountered this address on blockchain.info: https://blockchain.info/address/1CzpppydnGN5dQN7iBnZbmm5RXreu7hrHW and at the top a message appears presumably describing the owner of the address. I have not seen this before. Is this just a feature of blockchain.info or is it a feature generally available in the Bitcoin system? And if so, how does this feature work?
This is known as "tags", and it is 'blockchain.info' specific. You can use any web page, or bitcointalk.org user profile or bitcoin-otc Id as link. Your link page should contain your address.

http://blockchain.info/tags