Course evaluation is an integral part of a university's quality control process but it is also extremely difficult to get quality information from them. The best way to make sure the forms are filled in at all is to hand out papers in class and use classroom time to fill them in. On-line evaluation forms are notoriously difficult and returns are often pitifully low unless incentives are offered (eg fill in the evaluation and you enter a prize draw).
However millions of students are happily contributing to a completely voluntary evaluation tool called RateMyProfessors. This site claims to cover over 6,000 universities and colleges in the US, Canada and the UK and asks students to rate their teachers according to a variety of criteria such as easiness, helpfulness, clarity, textbook use and interest level. Lists are then compiled presenting, for example, a top ten "hottest" teachers, whatever that may mean.
This service is clearly controversial and is outside university jurisdiction (a possible reason for students' interest). Teachers may well feel unfairly treated and this is clear in the discussion forum on the site. There is an interesting feature called Professors strike back where teachers state their case on video.
Is this a case of positive consumer action or a place to get your own back on a teacher who gave you bad grades? Whatever it is it is definitely a factor to be reckoned with and it will be interesting if the phenomenon spreads to the rest of Europe.