The droves of disgruntled teachers and staff writing negative reviews are case in point, that criticism and feedback are critical in a system that regularly targets students and employs demeaning, intimidating educators.
Ratemyteacher is a decent service which allows the underrepresented student body to speak out and inform others of negative and positive experiences. My only complaint would be the lack of moderation, and how easy it is for offended teachers to take down reviews based on feelings alone.