Hubot supports IRC too (though probably not as well, we only hop in when Campfire goes down).

We depend on having a nice, customizable native Campfire client. We keep a custom js script in DropBox that Propane (http://propaneapp.com/) loads on startup. We've been able to modify the UI to show avatars, highlight successful/failed builds in Git push notifications, etc.

CF also gives us a few other nice features, like offline transcripts with search, and STARS.

Surely, you can do all this with IRC... and there are other chat apps that people like too. We're hoping that people add support for them to Hubot.