Another recommendation engine for comparison (Score 2, Informative)

Is Soundflavor.com. They let you build playlists and get recommendations, relevancy ranked, that would fit the mood/lyrics/style/etc.. of that list. The advanced search shows you a little bit about the characteristics they have on each song. No I don't work there, but I know people that do and find it very useful for finding music for a particular themed party or event. There is also a social networking component where if you "trust" other members' musical tastes your recommendations are changed by how they've rated different songs.