FB chat to me is basically real-time private messages rather than more traditional instant messaging, but everything I described except securely archiving the history could be done by FB transparently to the user. Of course you can do the work yourself, I just think it would be a nice gesture if FB provided the option to do the work for you, a way for the user to conveniently make sure FB keeps their parsers off the user's chat data. (It could also be extended to other data.) Also with how frequently Amazon prompts me for my password, I don't think users would be incredibly turned off by FB prompting for a password when they start chatting, and their browsers can be made to remember it anyway.