It's safe to say this isn't a question that's passing through your cranium on a regular basis. If it is, I pity you. I can also help you.
Audioscrobbler is a popular service which can track the tunes you're playing on your computer. While I work (and play) I'm often listening to MP3s from my collection. Thanks to the Audioscrobbler Winamp plug-in, you can see what I'm currently listening to and what I've heard recently. You can even see what tunes and bands I've heard the most and you can see who else has been listening to the same. It's awesome.
Visit Mike Boon's Audioscrobbler page for all this cool detail.
