The conversations/rooms in HipChat (in the Windows client, the web client, and the Android client at least) are ordered in the order you send/receive conversations or join a room. This makes re-using conversations difficult. For instance, if I'm searching for a Mike, I can't just go to the M's. I have to literally search through all my open conversations for the specific Mike I'm looking to talk to. He could be at any point in my conversation list.
It would make more sense if they were ordered alphabetically.