Start-ups have been trying to crack the music "discovery" problem for years. The problem is this: you know what music you like, and you have plenty of it, but it's usually very difficult to find new music in a similar vein that you'll also like. Pandora has one solution, but it's not the only game in town. There's the new MusicIP, for example, which is a lot more fun to explore because of its fluid, open-ended interface. It doesn't play complete tracks, so it's not a direct competitor, but if you're looking for new tunes, it's worth a spin.
MusicIP also has a local music player that looks a lot like iTunes. It does much the same thing as the Web site, but does so against the music on your hard drive. For people who have thousands of music tracks in their library, this is great, since it helps you find music you like that you might not even know you have. It's like closet shopping in your own archives.
While I encourage people to try this service (it's free and fast, what do you have to lose?), I should set expectations: The MusicIP library is still being built, and some of the recommendations are amusingly off-base, at least to my tin ears. Trying to find a match to Tom Waits' gravely "Clap Hands," for example, MusicIP came up with Fleetwood Mac's treacly "Sara." I don't think so.