User submitted content is one of the defining features of our new "2.0" world wide web. Sites that depend entirely on content produced by its visitors are being acquired every day and no frequent user of the Internet could have failed to hear about sites such as MySpace, Digg and YouTube. But user submitted content is of varying quality, especially when it expresses an evaluation of something, such as a review or a blog entry. It has become more important than ever to be able to tell quacks from the real doctors.