Wikipedia: the dumbness of crowds
The problem with the Wikipedia is that entries are of highly variable reliability and quantity. Due to the sort of people who contibute to Wikipedia, the entries on (say) Star Wars or the Klingon language are broader, deeper, more detailed and accurate than (say) the entries on relational database theory. In practice most of the entries on computing and related disciplines are reasonably reliable, because there are anough web users with relevant knowledge to correct obvious errors in their own fields (if they can be bothered).
Even so, unless you already know a fair bit about the topic it can be hard to determine whether the entry has been written by a leading expert or some passing nimrod. And when it gets to things like Latvian mythology, who knows? Is this entry on Tanis Diena, the sacred pig holiday a spoof? How would you find out, except by going to some authoritative (but less exciting) source such as the Encyclopedia Britannica in your local library? Even the Wikipedia founder says that too many entries in the Wikipedia "are nearly unreadable crap".
I am reminded of the chapter in "Surely you're joking, Mr Feynman" when Richard Feynman was reviewing physics textbooks for schools.
The man who replaced me on the commission said, "That book [that I thought was bad] was approved by sixty-five engineers at the Such-and-such Aircraft Company." I didn't doubt that the company had some pretty good engineers, but to take sixty-five engineers is to take a wide range of ability - and to necessarily include some pretty poor guys...It would have been far better for the company to decide who their better engineers were, and have them look at the book. I couldn't claim I was smarter than sixty-five other guys - but the average of sixty-five other guys, certainly!
Of course, there are some very good uses for the wiki technology. A prime example is the Extreme Programming Roadmap. This site is hosted by Ward Cunningham, who invented the Wiki concept as well as being one of the founders of XP along with Kent Beck. This wiki works because it is a site for sharing and exploring ideas. It is a conversation, an exchange of opinions, not a source of facts. It is precisely not an encyclopedia of Extreme Programming (eXPedia? or has somebody already got that?).
Wikipedia is predicated on the assumption that knowledge works like some kind of pachinko machine: the channel where the most balls go must be the truth. But actually all you end up with is a lot of balls.