I've said it before and I'll say it again: Knowledge is of two kinds, you either know it or you can find it on Wikipedia. This article discusses a study by Nature that took scientific, complex articles from both Britannica and Wikipedia and had them reviewed by experts. The result? Wikipedia and Britannica are reasonably close - the surprising thing is, they both had four "major" errors in 42 articles. Not a good hit rate for Britannica!
This is of course in sharp contrast with the recent kerfuffle over Wikipedia's accuracy and peer review process.