I just discovered Pandora. It is a online flash streaming music player that plays the music that you like much like last.fm radio, just simpler and with instant feedback. You simply go to the site and tell them what artist or track do you like and the music starts playing in a Flash applet. Then similar music starts playing and you can say whether you like this particular song or not. There are even keyboard shortcuts, so it is enough to focus the windows with the player and press "+" if you like the song or "-" if you don't and it immediately adjusts its playlist to your input. Those kinds of services could replace downloading of music via BitTorrent for most of "background noise" kind of use.
Update: now that's one screwy service. After you listen to a bunch of songs, the player stops and requires you to register. It gets even better - the registration is US only. Just great! Well - back to last.fm radio to me.
Update2: Oh, ok - you can easily register with zipcode of 00000 and no paying for the service is required. And I also have heard some hreat music there, like the Bohemian Rhapsody that fills my earphones now.