I've only heard a couple of mash-ups. A few questions; - Are they more of a European phenomenon than US? - Have you heard any you've liked? (I thought the mash-up I heard of "Smells Like Teen Spirit" and "Bootylicious" was pretty good). - Do you think they're musically valid or just another indication of the sick state of the music industry? Any other comments you'd like to make about them are welcome, too.