If you'd like to get a visual alert every time a new message is posted in Campfire (one that's visible even if your browser window is not), then check out this bit of code Snailbyte cooked up. It uses Tinder, an API for interfacing with Campfire, to create an activity notifier for KDE (the knotify method can be replaced with a call to Growl for Apple users).
For Mac users, Pyro also offers this functionality (and a lot more).
Your Campfire chats in a dedicated application, with the number of unread messages on the Dock icon, in Growl and on the Campfire tab bar. Drag and drop file upload. Accelerated room switching. AppleScript support. Pyro for Mac OS X 10.4 does all that, and is completely free, so download yours now!
You can also use Tinder to hook Campfire up with Subversion, Trac, and Capistrano. More on Tinder.
