All registered users already have an email address associated with their account.Add "Enable e-mail from other users" to user prefs.
Other reasons why it should be easy to send a private message to a member: But above all, I really dislike seeing comment threads that have in-jokes and personal chats. It's a Q&A site and this strongly encourages that all answers and comments are part of the record rather than, say, the OP and someone else getting into a private chat and solving the problem to the benefit of noone else. The biggest weakness of the current system is that someone can leave a comment on one of your posts, you essentially reply to them and theres no way to bring this to their attention (unless they've subscribed to the question, which lets face it doesn't happen).I had asked a question and was in the process of trying to find an answer with a particular user (user A).In the course of working it out with user A another user (user B) came a long and offered the exact answer I needed. Shortly afterwards user A posted the same answer in a comment.If such a thing existed it would be easier to contact User A in order to explain that I had meant no offense by accepting User B's answer and that I greatly appreciated his help!Well I think there isn't any IM sort of mechanism as of now.