Snopes.com ("Urban Legends Reference Pages") regularly discusses various Internet rumors, chain emails, and "other such stories of uncertain or questionable origin". The WP entry reads like a press release, and one might assume that they've never gotten anything wrong. In fact, the closest it gets to anything that could be considered in any way negative is the statement that "not all of their sources... are fully verifiable".
A look at the Talk page will reveal a section called "It's almost like they never get anything wrong!" which I can confirm was meant sarcastically, since I wrote that title and provided these two links illustrating errors Snopes has made: link, link. Neither of those links has never been incorporated into the main article as far as I know; perhaps they're waiting for the MSM to confirm easily verifiable facts. See the 'snopes' tag at the first link for more.
And, on the Talk page someone else has provided these two links; presumably there's some difference between them:
In January 2006 the neutrality  of the main section was briefly disputed, but that appears to have been "resolved".
It had a "Criticism" section for a few months , but that doesn't appear to have ever contained specific examples of their bias or incorrect "debunkings", and it was eventually removed in September 2006 .