Bit difficult to do a search for this, so we'll see if this dies a horrible, painful death.
Basically, you download the plugin for whichever media player you use to play stuff on your PC, and it keeps a log of everything you play. Only music, for all those who enjoy a little porn, no need to worry. Dunno if anyone else uses it, but if there's enough interest then there could be a group started for the entire forum, which would keep a record of the tracks and bands that are most popular among the peeps each week.
After you've played enough tracks of your own it also opens up the chance to listen to similar bands to those on your playlist, and I've discovered a few pretty cool new bands from that in the last couple of months.
Plus you can find out who's secretly listening to Hanson, and mock them.
http://www.last.fm/user/franscar/
That's mine, obviously. Use the menu at the top to get to the homepage. You knew that.
EDIT: Look, musicbanter now has its own group. Join it.
http://www.last.fm/group/Musicbanter.com