Audioscrobbler!

Check out Audioscrobbler. You sign up, then install a plugin for your favorite music player (pretty much everything is supported - Winamp, XMMS, Windows Media Player, iTunes, etc.) and it updates what you've been listening to recently, and does some neat statistics and so on. And it puts this on the web for all to see. Which could, of course, be a bad thing if you're a closet Backstreet Boys fan or something, but that's your problem. It's fun to see what your friends have been listening to recently, and giving it a listen if it's something you haven't heard before. My profile is at http://www.audioscrobbler.com/users/vokyvsd. Give it a shot.