James Tauber on threaded Instant Messaging. (Building something with PyThon and JabBer!) I was just thinking about this the other day. Even having just enough structure to make it clear which previous item a new blit is referring to would be handy (when 2 people are going back-and-forth quickly, even sticking to a coherent single topic, it can be tough to tell what's in reaction to what).

Update: he added a link to a list of other tree-based IM clients.

User Options Recent Changes Help Page