Back to wikipedia... Nature has an article on wikipedia vs Britannica. It was an interesting exercise, and as the most notable climatologist on wiki :-) they interviewed me, which lead to the sidebar article "Challenges of being a Wikipedian" (see the Nature article; click on the "challenges" link near the bottom). It contains the rather nice quote from Jimbo Wales "Connolley has done such amazing work and has had to deal with a fair amount of nonsense" (does Lumo still read this?).
What Nature did was to take a number (50; of which 42 came back usefully) of wiki and Britannica articles, and send them out to experts for review. There was a fairly severe constraint on this: that the articles had to be of comparable length in the two sources; which is why I think no climate change type articles were done. I strongly suspect that if you try to find anything about, say, the satellite temperature record in Britannica it will either be entirely missing or badly out of date. The list of articles is here.
There were 8 serious errors in both sources. Then we move onto more minor inaccuracies. The oddest thing about this is that the average number of errors in Britannica is 3 and wiki 4; and Nature (genuinely) expected us to be *pleased* about this, as though being nearly as good as Britannica was something to be happy about! I rather suspect that this may be due to the choice of articles to some extent. The GW articles don't contain many errors (except the septic cr*p, sadly we can't get rid of it all :-().
The most pleasing part, though, is the accompanying editorial which actively encourages scientists to contribute (James, are you listening?): Nature would like to encourage its readers to help. The idea is not to seek a replacement for established sources such as the Encyclopaedia Britannica [oh yes it is... WMC] , but to push forward the grand experiment that is Wikipedia, and to see how much it can improve. Select a topic close to your work and look it up on Wikipedia. If the entry contains errors or important omissions, dive in and help fix them. It need not take too long. And imagine the pay-off: you could be one of the people who helped turn an apparently stupid idea into a free, high-quality global resource.
[Update: there is a Nature blog here and this includes a list of the errors in the EB and wiki versions; see-also [[Wikipedia:External_peer_review/Nature_December_2005/Errors]]. The Nature blogs report on Jimbo's visit is interesting too. And [[Wikipedia:Requests_for_arbitration/Climate change dispute 2#Removal of the revert parole imposed on William_M._Connolley is nice to have...]