This guy has some pretty hilarious views; my favorite of which is that he believes that Jim (or as he calls him "Jimbo") Wales (a co-creator of Wikipedia) is fictional. He demonstrates this with an image of Jim Wales which has been photoshopped to include the word "fictional" above it in rainbow letters.
All jokes aside, there are clearly some issues with Wikipedia. According to Zeitgeist the 9/11-entry on Wikipedia is on a watchlist, in part due to the fact that "contributors to Wikipedia... have tried repeatedly to insert anti-Jewish 9/11 theories into Wikipedia's pages and represent them as fact or at least plausible versions of reality." One less serious instance of vandalism is that of the entry on Sacha Baron Cohen. A commenter on Tribe.net reports that according to one edit of the site Cohen is"Orthodox, bisexual, and marrying the hot redhead from 'Wedding Crashers."
Despite Nature's study that Wikipedia is nearly as accurate as the Encyclopedia Britannica (4 errors for every 3 in EB), it is commonly viewed to be inaccurate, or flawed. In one conversation on Wizbang, a contributor retorts "where did you get that statistic? Wikipedia?"
This is not to say that Wikipedia is useless, or totally inaccurate. I have learned many a useless and interesting fact (subject to confirmation from an outside source), mostly about aircraft carriers. It can also be used for a higher purpose than time-wasting. Mobius of Jewschool created a "Jooglebomb"--a "googlebomb" (notice that I used Wikipedia for the explanation. Ironic, eh?) whose goal was to make sure that the first hit on Google for the word "Jew" would be the Wikipedia entry (as flawed and controversial as that may be) instead of straight up anti-Semitic websites.
Long story short? Use Wikipedia with discretion, the way you would an encylopedia, as a starting, and not an ending point for your research.