Richard Jones, one of the co-founders of Last.fm, has a writeup describing how Last.fm uses IRC. I’d really like to see IRC used for more stuff like this, including communication in general. (In the comments, one guy describes how him and his friends use their own private IRC server for communication.) It’s sad that a lot of people don’t even know what IRC is, let alone use it. If you’re one of those people, check out The IRC Prelude and the Wikipedia page. If you’re using Windows, check out the free mIRC client (I use irssi on Linux) and if you don’t feel like installing anything, check out the awesome web-based client Mibbit.