Jim Felton, a Finance prof at Central Michigan did a study of student ratings of faculty on ratemyprofessor.com.
He found students' evaluations of their professors was pretty highly correlated with how easy the prof was perceived as being (correlation of 0.62).
However, begin percieved as "hot" (physically attractive) was even more highly correlated with their evaluations (correlation of 0.64).
I try to work my students as hard as possible, and I'm far from a stud muffin (but I did go 18 miles on the bike last night in under an hour, so there!) So I guess that means that if I get good evaluations, they're for real.