There have been several posts here on Vital Signs alerting visitors to the problems of inaccuracy and bias to be found at Wikipedia --Reader Beware; Wikipedia: Reader, Beware II; and Wikipedia: Still a Bastion of Bias and Error.
Now, Matt Sanchez, blogging over at PajamasMedia, explores the matter again (particularly as it applies to America's upcoming election) in "Wiki-Whacked by Political Bias." Check it out.