Users rate how good a job moderatorss are doing. The most famous site with such a feature is Slashdot. Users can enter "meta moderation mode" (or something similar) and will be shown a post that was moderated in its original form, and the nature of the moderation. The user then decides if the moderator acted fairly or not- and if not, in what respect the moderator was wrong. This information is used to improve the quality of moderation on the web site.