In my experience this has been good for weeding out really bad profs. At my Grad school they turfed a prof 1/2 way through that was bones bad.

That said - it's perverse at the other end and I do believe that there is unconscious sexism.

We had a really smart bunch of people, and some of the female teachers were a little more apprehensive in front of us which I think signals to people subconsciously.

Another way: the feedback has to be interpreted.

I suggest that the profs should not be 'graded' by students - rather there should just be an open ended opportunity for feedback.