OK, so you probably don't want to do this for internal projects (CCTray works great for that), but if you've got an open source project and you're using CruiseControl.NET then it might be an idea to let your community know about it.

You can't have them all downloading CCTray and pinging away at your server all day, but you can let them listen to a Twitter feed of your build notifications. If that's something interesting for you, then have a look at the Twitter Publisher for CC.NET.

At long last something useful to do with Twitter.