My attention was drawn by the LITA-L discussion list to an interesting article in Nature on a test of Britannica and Wikipedia. Nature sent out a total of 50 articles from the two encyclopedias for peer review and concluded that there was not much to choose between the two.
Only eight serious errors, such as misinterpretations of important concepts, were detected in the pairs of articles reviewed, four from each encyclopaedia. But reviewers also found many factual errors, omissions or misleading statements: 162 and 123 in Wikipedia and Britannica, respectively.
As a result of the recent fuss over misleading articles in Wikipedia, some changes are being made. Specifically, 'stable' articles will be identified and will not be editable - only a separate version will be editable and that will replace the currently 'stable' version when it is deemed appropriate.