On October 9, 2008, and the days leading up to it, every business reporter on the networks reported that it was the one-year anniversary of the first time in history that the DOW broke the 14,000 mark. This, after all, was easily checked on Wikipedia, which was saying at the time that it broke 14,000 for the first time on October 9, 2007..
The DOW actually broke 14,000 for the first time almost three months earlier, on July, 19, 2007. This fact could have easily been checked--at the original sources--by the business reporters or their support staff without ever leaving their browser-windows.
I'm sure the ANONYMOUS contributors to Wikipedia didn't intentionally get it wrong. Sometimes they just get distracted, for example, when their moms call them down for dinner.
Update: Recently, wikipedia falsely attributed some horribly racist quotes to an American talk-radio host named Rush Limbaugh. The biggest media outlets, including ABC, NBC, and CBS, all reported the phony wiki quotes as if they had been a fully fact-checked news story. It is much harder to ignore the possibility of malice on this one, and claim that the anonymous contributors were merely suffering from distraction.
On the other hand, the individuals in the media who reported the wiki-fictions as news, could simply be labeled incompetent. Most would agree that it is better to be incompetent than to be a slanderer.