While I've been a happy gaim user for some time, I miss the threading feature of email. If I am discussing several topics at the same time with someone, it's not clear which topic an individual message addresses.
I can't think of a convenient user interface for threaded IM, however. Perhaps the program would show, for each thread, all messages less than some age? The user would select a thread before responding, perhaps with the most recently responded-to thread selected by default.