not a bad idea, Doug... it's just that I don't think people can really put their finger on (and thus be able to articulate) what exactly it is that they like about a particular piece of music... and I doubt AI could really do that for them -- "mellow Beatles" may give an idea but I suspect quite a few songs that would fit that description (when you analyze the music) would be disappointing to quite a few of those searching using that criteria...
P.S. also, if you expect it to be a cross-cultural tool, I would think you'd run into quite a few translation/culture issues
P.P.S. I'd be really impressed if actual appeal of a song could be predicted (e.g. being able to say that "Dragostea din tei," for instance, would have huge appeal to so many people coming from so many different cultures just by analyzing the song...) D.