Here's a pretty interesting article on this year's Presidential election and the in-fighting on Wikipedia.

Collaborative history is a wild ride, as the recent presidential election demonstrated. In October readers were editing and re-editing the entries for President Bush and Senator John Kerry at breakneck speed. And some of it wasn't exactly editing. If you clicked on a picture of Bush in his National Guard uniform to get an enlarged version, you would see a picture of Hitler.

...

Surfacing from the editorial whirlpool, I wondered what had happened to Senator Kerry's entry in the Wikipedia. Two days after the election his entire entry had been replaced with a single line: "John Kerry is a girl." It has since been fixed.

Nice.

Wikipedia is a pretty interesting social construct, and demostrates pretty well the limitations of unmoderated or semi-moderated content on the internet.

But I've used it quite a bit and not seen any irregularities. It's a pretty damned good source of information, and I find myself using it more and more. Just like writing a term paper in school, I'd never use an encyclopedia, much less an open, collaborative one, as a sole source, but it's a pretty good place to start if you need info on a topic.