The web client is a bit "special" though - after a day or two of running it with 4+ channels open the history will build up and jquery functions will start freezing the interaction. Flash/AIR client is much better, but... it's Flash/AIR (copy/paste issues, different set of fonts, message notifications not clear).
The best way to access hipchat that I've seen so far was just a jabber client - xmpp seems to be the backend of their service.