Personally I think a lot of the films mentioned here as being really bad, such a waterworld and BE, actually aren't that bad. Certainly not high points in cinema history but not every film can be.
Having said that I think film rating sites give an excellent lesson in why many statistics should generally not be believed and statistics gathered on the internet particularly so. Pick just about any film and look at the rating on IMDB and Rotten Tomatoes. Make sure there is a decent number of votes on both sites, lets say 10k votes. The scores will almost always be wildly different despite what you would think would be enough votes for a representative sample. Consider the many psychology experiments look at just small groups students and you have to wonder what they are really discovering.