Snopes.com seems to be one of the most trusted sources of information available (after Cecil, obviously). Have they ever gotten anything wrong? That is, has any explanation by Snopes ever been incorrect (not just incomplete)? Have they ever had to reverse their position on something?
Well, considering Cecil is a group of people as opposed to a person, I’d put Snopes and Straight Dope on par with each other. As for your actual question, I too would like to know.
I can’t recall seeing a retraction. They are pretty thorough.
It has happened… It’s about as rare as it is for Cecil or The Bad Astronomer.
Remember, these guys are beloved for their integrity, not their omniscience.
Trinopus
Sure, they’ve changed their minds about particular stories as new evidence has come to light. I can’t remember their exact original rating for it, but (as for many of us) their take on The Newlywed Game story was pretty sceptical until a tape of it finally turned up.
Snopes extended an apology to Michael Moore a while back. It concerned a piece Moore had written about the government flying relatives of Osama Bin Laden back to (I believe) Saudia Arabia in the days following 9/11 when commerical flights were grounded. It turned out that most of what Moore said was true.
The Mikkelsons actually consolidate the general knowledge of the alt.folklore.urban newsgroup. This group is pretty good at researching, plus on most legends that have been around a while, they’ve just had time to get many inputs.
A recent exception that I can think of is the famous quote from the Newlywed game, which UL researchers maintained for a long time to be false, until someone came up with a copy of the episode.
Snopes was originally wrong here also.
Duderdude2, Cecil is most certainly a person.
And by the way, Snopes himself used to occasionally contribute to the alt.fan.cecil-adams newsgroup. I recall specifically a thread about the monetarist interpretation of The Wizard of Oz, in which I was wrong and he was right. In Snopes’ old newsgroup postings, sometimes the most entertaining part was his .sig.
But Snopes isn’t a person, CurtC
A long time ago, they used to have made-up stories in order to teach their reader’s a lesson about trusting sources. I remember one story claiming “Mr. Ed was really a zebra.” The point was that you shouldn’t trust anyone, not even them.
They must have gotten flak for it, because it eventually moved to a portion of their website that clearly indicated “the stories that follow are made up,” but the linked pages themselves were unchanged. That was about a year ago.
I don’t think the pages are still on their server (I just did a search for “zebra” and didn’t get any hits).
David P. Mikkelson is snopes. His wife Barbara also contributes to the site.
Sorry for the nitpick CurtC, but David P. Mikkelson is David P. Mikkelson, not Snopes.
I found the zebra story - it’s in the section called Lost Legends. (They don’t seem to index it, but they have a link from the main page). A note to anyone reading these - check the section marked “Additional Information” if you’re the credulous type.
As for Cecil, he’s certainly expanded on an answer or two, but I don’t recall him ever being wrong. 
He posts on USEnet using the name “snopes”, as seen here.
Cecil was wrong on the Let’s make a Deal question, but of course he ended up admitting it.
Hate to do this, but got a cite for that?
Cecil also admitted he was wrong about the five ways to get to first base without hitting the ball. Took him 14 years, though.
Didn’t they get the “lawyer jumping through the window” story wrong at first too? I can’t recall but I seem to remember some controversy around it.
The name Cecil Adams does not, and has never, referred to an actual person. It’s trademarked by the Chicago Reader. There have been a number of different "Cecil"s over the years.