That's a good recommendation. I have a feeling it wouldn't change the results much for pop songs.

I know Pandora has done some analysis like this for their database, but I thought it was limited to things like major or minor tonality, upbeat tempo, etc. and didn't delve as much into the nitty gritty harmony. One reason for this might be that these patterns are so universal (spanning lots of genres), that it might not be too helpful for determining what types of music people like. I could be wrong about this though.