I've been listening to Pandora internet radio. The product is a preferences engine and a web-based radio. You make your own radio stations. Pandora plays songs; you train it to play stuff you like. (I have no idea what the company is trying to be. I doubt they're making a good living off the ads.)
Today it just “clicked” and started playing song after song after song that I liked. Mostly stuff I had never heard of before.
It has been a little frustrating, in part because you can't just tell Pandora what musical qualities you're interested in. Instead you have to list musicians or songs that you like, and fine-tune it by giving a thumbs-up or -down on individual songs. For me, this is much harder. Trying to teach it what I want on my "Jazz" station (mostly piano instrumentals, some artsy orchestra pieces, and a few songs by Billie Holiday) has so far been futile. Perhaps Pandora can't model my preferences. Or maybe it just needs more time.