Internet encyclopaedias go head to head -- This article in the prestigious journal Nature compares the accuracy of science articles in Wikipedia and Britannica. Britannica wins, but not overwhelmingly, with about 25% fewer errors in the average entry. I would assume that the worst Wikipedia entries are probably ones dealing with sensitive political issues, especially relatively obscure historical or philosophical material that happens to be relevant to the massive slugfests over abortion, Israel, Bush, etc.