Wikipedia has become one of the biggest forces on Google: most basic searches bring results from the online encyclopedia back very high, often in the top two or three positions.
But the result has not just been more traffic - it has been more pollution, especially as unscrupulous individuals (spammers, nasty search engine optimisers etc) try to game the system. After all, even if a spam link lasts just a short while, Wikipedia's high ranking and open format means it can be a successful way of gaining exposure.
As a result, the Wikimedia board has decided to use Google's "nofollow" attribute for all links out of Wikipedia. Brion Vibber makes the change via this email, and you can read a following discussion among Wikipedians about the decision:
Having been requested by Jimmy to do so, and having seen a fun rumor of a "search engine optimization world championship" contest targeting WP[1], I've gone ahead and switched rel="nofollow" back onto URLs in en.wikipedia.org's article namespace.
Nofollow was inaugurated two years ago by Google as a way of combatting comment spam on blogs, but now it's a crucial tactic in trying to dissuade spammers from abusing entire sites, and search engine listings themselves.
(By the way, there are more details on the 2007 SEO World Championship here - the best optimiser wins a car)
