Pandora, if I'm remembering correctly, also has a feature that Spotify lacks, which is to say "I don't like this" for a piece that it chooses. Although I couldn't say how much that influenced its later choices, it feels better as a user to be able to convey it.
I know for several of my "stations", they kept trying to suggest Coldplay. I'd constantly give them the thumbs down as I didn't feel Coldplay matched what I was going for. It didn't seem to affect their later suggestions.
