I was surprised when I went to Pandora and searched for "Soundgarden", and not only got a lot of Soundgarden songs that I like, but a lot of other bands such as the Red Hot Chili Peppers, Stone Temple Pilots, Audioslave (not really surprised, seeing as it basically is Soundgarden), among other bands that I really like.
If you're not on your main computer, or simply can't access your music, this is a great alternative. Last.fm is another good example, but Pandora does give you good alternatives to music you like.
No, I usually use Last.fm, but I might try it out.
I love Pandora Radio.
It's a great way to discover new music.
Pandora also has a great application for the iPhone/iPod Touch.
Nah, it doesn't have a lot of the stuff I like, and I prefer listening to what I want, not just suggested stuff. At least the likes of di.fm are consistently good with the genres, especially hardcore and gabber.