The Gale chat system uses categories, which can be created on the fly; they're like a cross between newsgroups and IRC channels. A Pan-like threaded interface might make it easier to follow threads of communication; some history (say, a fixed time period's worth) could be shown, along with "new" puffs in a thread. (The disadvantage being that you have to keep track of which puffs have been seen, of course.)
It's a pity Gale doesn't have an equivalent of the References header.