Pandora reminds me of Yahoo's LAUNCHcast, another music streaming application that also lets you rate the music. LAUNCHcast, though, chooses music based on the ratings of other LAUNCHcast listeners instead of on the music's physical qualities. It is similar to the way Amazon.com recommends books and music to you. This approach is a little more interesting to me because it can be full of pleasant surprises. For example, if there are many people out there that like John Coltrane and also like Tribe Called Quest, LAUNCHcast might play Tribe Called Quest for me if I rate John Coltrane highly even though the two artists' music don't have a lot in common physically. There just may be some unexplainable reason that people who like Coltrane also like Tribe. Pandora would never be able to make that association. Instead it would keep playing saxophone-centric jazz from the 60's.
The major drawback for LAUNCHcast is that it only works on Microsoft Internet Explorer browsers. This means I can't use my favorite Firefox browser and, even worse, I can't listen to it on Linux, which I use at work. Pandora, on the other hand, is a Flash application so it works in Firefox and on Linux!