I was making an IRC plugin for IDEA but now I don't have time even to finish the configuration UI. At the same time I feel that this project may be interesting to someone, so I decided to share what was already done: http://www.intellij.org/twiki/bin/view/Main/IdeaIRC
Feel free to contact me if you wish to take over.
Technical details: uses PircBot as an IRC engine, PicoContainer as an IOC container. Has UI abstraction layer which allows to have both IDEA and standalone Swing versions without a lot of overhead.
Highest priority tasks: finish configuration UI, fix autoscrolling bug. After this it will be generally usable.