I really don't like Pandora!! Computer automated radio (The Music Genome Project) seems like it would be awesome because it starts off on a song or band I like, but then it spirals into something totally shitty because it shares superficial characteristics with "the stuff" I like (gender of lead vocalist, level of distortion on the electric guitar, type of background vocals). Instead of getting turned on to new music, I end up irritated and skipping over songs like an impatient, petulant child. Because when it comes down to it, it's the SONGS, not elements of songs broken down into vague classifications, that make for good listening.
This is why I'm newly into this handy playlist app Songza. You log in and it takes into account the day of week, time, and possible moods and genres that you can listen to. Since it's all playlists compiled from their "music experts" (they even have a section called "record store clerk"), it's a pretty decent way to pick what you want to listen to based on your mood, the genre, and the time period. Check it out especially if you wanna get this sick 90210 playlist! You're welcome!