When the web site, RateMyProfessors.com, was launched six years ago, most academic insitutions viewed it as an occasionally hurtful but harmless outlet for student opinion. But the site, on which students at colleges and universities around the world can evaluate their teachers’ performance with impunity, has grown to the point that it is now affecting class enrollment at some schools. Professors and administrators hate the site, and lawsuits are regularly threatened against its owner. But the site is far from a vitriolic free-for-all, with positive comments outnumbering negative ones, and a group of volunteer “student administrators” assigned to keep an eye on verifiable claims.