There are many myths and truths about the value of student's evaluation of a course and of a teacher. There has been a long discussion on what can be done with the information given by these evaluations, from the complete dismissal to the partial adherence to the suggestions and criticism given. An excellent article is that of Ken Bain http://www.montclair.edu/academy/services/white.html which is summarized in his book "What the Best College Teachers Do." Bain's assertion that comments and ratings by students are useful providing valid and reliable information is based on an extensive literature. But the question has to be re-address to how these end of course evaluations are structured and to the care on design and intentionality that the questions in the questionnaire are addressing. The most important thing according to James Lang (On Course p 277) is to ask the student questions that will help understand their learning advances not about any personal characteristics of the individuals involved, being the student or the teacher.
In this respect it looks like the end of course evaluation forms have to be adapted for individual courses and have to be reviewed periodically to accommodate to new forms of instruction and instruction technologies.