Just discovered the website - Pandora. Basically, it allows you to create a streaming music station by typing in the names of some songs or bands that you like. It will then play you music by those artists and similar ones. It is great for discovering new music and re-discovering tunes that you have heard on the radio but forgotten who they were by. Currently it is free and also free of audio adverts. They also offer a subscription service which will remove all commercials. Pandora is currently only available to people in the US. I'm in the States at the minute so I can't tell if it is doing any IP resolving to determine location or it is just using the ZIP code which you enter on registration.
At the risk of inventing a new Web 2.0 buzzword, the interface could be described as FLAX (FLash and Xml) - it's pretty nice and does a good job of masking the restrictions imposed by the music licensing deals that the company has struck.
If you (like me) spend a lot of time tied to your computer then this is an ideal source of background music. So far I've done a couple of quick "Stations". A relaxed one and one full of pop. Be warned, I like my music like my movies - unchallenging. However, thanks to Pandora this is changing and I'm listening to stuff I would never have thought to buy myself from iTunes.
It is pretty good - I'm creating a ^metal^ one at the moment (^_^)
Well, I'm in Japan, and decided to try to satisfy your curiosity about whether they do IP checking. Seems to work ok for me, so I guess not!