This could be just available as an option.

But it is very helpful if in a muc and maybe even 1-1 chat if a line is drawn at end of all read messages.

So now if chat window is active and then i switch to say firefox and then back to chat window then there is a line which separates the old messages and the new messages which have been received since the last time the window was active.

This could be very helpful for irc chats.