Maybe not even a worthwhile to you selection click but a comment feedback option. Name of the Commenter and the Comment. I'd find that more useful.

daveasdf - kicka** riff man!
AndyP - you must be just starting out dave
daveasdf - yeah!

or

AndyP - decent use of chromatics to strenghten the pinky


maybe have them under the individual riff links and the riff writer's definition. but then you'd probably get a huge forum under each riff submission.