You get your own online music profile that you can fill up with the music you like. This information is used to create a personal radio station and to find users who are similar to you. Last.fm can even play you new artists and songs you might like. It's addictive, it's growing, it's free, it's music.

[ Memestreamer (and roommate) ophten sent me this link a few days ago and I've already found it to be quite rad. The more people use it, the better it's recomendations will get, but already I've got a list of artists to take a look at based on proposed similarity to things i like.

Best of all, it's trivial to use... you install the audioscrobbler (worst. name. ever.) utility, and just play music via iTunes, Audion or if you're not yet a mac user, XMMS, winamp, etc. The utility pays attention and just uploads the data to build your profile. I haven't gotten into the "personalized radio" bit yet, but i'm looking forward to giving that a shot this (long! w00t!) weekend. -k]

Last.fm