Have your read the article about facebook storing records of your deleted messages ? What about chats that you never wanted to retain?
Recently I have this idea popping up to my mind. The idea is to encrypt and decrypt all the (private) messages on the client side so that everything the sever stores is inherently worthless unless "something" is provided to decrypt it at the user's end.
So I have done exactly that. By encrypting the messages on the client side it's guaranteed that the information stored by facebook isn't accessible by anyone, facebook included, except for the two parties involved.
Demonstration:
Download here