I love this site and service.
It uses a program called iScrobbler and will upload and update my iPod and iTunes tracks. (it feeds of the "recently played" playlist. ) It will update multiple computers and iPods also. )
You can also link to your playlists.
You can also use their player to listen to others playlists, which come through as "Radio Stations"
There are forums, and you can have a journal and friends, etc.. but I don't use all that jazz.
Just thought some of you geeks might like it.