I think it's a great idea. some of the best teachers I had where a real pain back in the day. they expected a lot from me and wouldn't except mediocre work. looking back I can see what that did for me and how much easier it would have been for them to play the buddy and let me slide.
now that I'm older and don't know all there is to know in the world, it's kinda cool to be able to go back and geve them some recognition.
it would be nice if they seperated the vote into catagories( curent or recient student, or alumni). it would be interesting to see how many teachers who get trashed by current students get better reviews by those looking back.