Earlier quoted context omitted.
I've determined independently that a IRC server fills a sweet spot in the collaborative toolset. A basic IM system isn't good enough because it doesn't have channels, it doesn't give you a shared history. Email is heavy and induces people to spend too much time per message. Sometimes it's good to have a light/noisy feed, and IRC is just fine for that job.
Checkout HipChat. Like IRC and has a desktop and web client. They also have API which you can use to post messages to channels from external sources. We have our Capistrano/Ant scripts post their status to our "Deployment" channel. Currently working on a bot that hooks into Jenkins so we can build via our "development" channel.
The Air app for desktop can sometimes have performance issues for no particular reason. They're about to release a native OS X app though so that should solve this for a large amount of users.
The android application in woeful. It consistently logs me out and forgets my password which means that it's totally unusable for out of office notifications from people. I've had to rely more on their email notifications for unread personal messages than their Android app. It's a real shame because I could see myself getting a lot more use out of Hipchat if it worked well enough.