In line with Berno's link (http://www.roughtype.com/archives/2006/09/a_fork_in_wikip.php), here are two of the better of many, many articles which have tried to get to the bottom of how Wikipedia manages to stay coherent when so many other crowd sourcing projects ultimately become little more than gibberish.
Slate traces the history of wikipedia through the Jesus entry: http://www.slate.com/id/2281294/
Spiegel has a long article which explains the inner workings of the wikipedia process by looking at the entry for the Danube Tower: http://www.spiegel.de/international/germany/0,1518,690402,00.html