Nice! I was thinking of adding a feature like this to my animated-guitar-tabs site Soundslice (http://www.soundslice.com/). I've got time-synced data for each note in a song, with string and fret values, so I'm planning to do stuff like "cliche lick" detection. Searching by riff would be a great addition.

I talk about this a little bit toward the end of this tech presentation I gave: http://37signals.com/talks/soundslice

I definitely echo what some other comments have said -- if you made it based on intervals instead of "hard-coded" notes, it'd be a lot more flexible! That seems to be how our own brains store music -- if somebody sings "Happy Birthday," for example, you can instantly join in, regardless of what key it's in. Unless you're tone deaf... :-)