Nature has a special report at http://www.nature.com/news/2005/051212/full/438900a.html , detailing the results of an accuracy comparison between WP and EB. While the Wikipedia articles often contained more inaccuracies than Britannica's, they don't look at the article sizes in each case. With Maveric149's help, I did:
http://en.wikipedia.org/wiki/Wikipedia:Village_pump_%28news%29#Nature_follow...
Result: Average article size for Wikipedia: 6.80 KB; Britannica: 2.60 KB. Number of errors per 2KB for Wikipedia: 1; Britannica: 6.
Put another way: Wikipedia has 4 errors to their 3; our articles were also 2 1/2 times longer on average.
Can someone please check my math, I did this pretty fast, and was half asleep :) It's not 100% accurate, but I was only going for a ballpark estimate. Note: we copied the displayed WP text, not the edit box text, and removed the TOC, See also, references, external links, and any other big tables or lists. The WP text came from just before the Nature article was published.
Raul654 and I separately submitted stories to Slashdot, and I would suggest anyone willing do something similar. The more requests they have for this, the more likely they are to accept it.
brian0918