I started to toy with
last.fm today. But I'm too lazy too figure out what it's all about and tell you about it. All I found out so far is that you can listen to music grouped by "Tags" ("powered by"
Audioscrobbler) and that they have a native last.fm-enabled music player for FreeBSD. So far so good.
There's also a plugin for
Serendipity which shows you what songs I last listened to and such (It's called "Audioscrobbler Plugin"), see the right column...