It's a streaming music service that has been hugely popular in Europe but has just become available in the U.S. Go to www.spotify.com, sign up, and request an invitation to the free service. You'll get one within a day. Follow the link in the email, download the Spotify client to your computer, and you're in business.

Basically, you can listen to any if the music in their extensive library for free in return for listening to the occasional ad. Very occasional. I think I got one ad in the course of listening to 20 or more songs. There's a paid version that gets rid of the ads and lets you download songs to your iPod. You can also upload music you own to the cloud, but I don't think I want to do that.