A scholarly article was just published comparing the student evaluations on Ratemyprofessors.com and those administered by universities.
Here is a snippet:
'You’ve heard the reasons why professors don’t trust RateMyProfessors.com, the Web site to which students flock. Students who don’t do the work have equal say with those who do. The best way to get good ratings is to be relatively easy on grades, good looking or both, and so forth. But what if the much derided Web site’s rankings have a high correlation with markers that are more widely accepted as measures of faculty performance? Last year, a scholarly study found a high correlation between RateMyProfessors.com and a university’s own system of student evaluations.'
And, like Tyler over at MR, I say, "go, Web 2.0!"