I'm a big fan of Wikipedia, and of course traditionally (like anyone) have been an admirer of the Encyclopedia Britannica.
Recently the highly respected magazine Nature published an article describing a study in which they compared the two and found only slightly fewer inaccuracies in Wikipedia than in Britannica.
"The exercise revealed numerous errors in both encyclopaedias, but among 42 entries tested, the difference in accuracy was not particularly great: the average science entry in Wikipedia contained around four inaccuracies; Britannica, about three." (from "Internet Encyclopedias go head to head")
Of course, Britannica is not about to take this sitting down. This is from their web site:
"Recently, the science journal Nature published a study of online encyclopedias. It was misleading and wrong from top to bottom, and in a thorough analysis of the evidence by our editors and their outside advisors we explain why the study was invalid and should be retracted." (from Britannica Web Site)
All this was covered in the Boston Globe this morning. Interesting.