The poll was conducted by Public Policy Polling. Here are the details, including crosstabs. http://www.publicpolicypolling.com/pdf/PPP_Release_National_1119.pdf The Wall Street Journal has rated their accuracy as high.
FYI: The original blog about the poll is here: http://publicpolicypolling.blogspot.com/2009/11/acorn.html The full results as a PDF are here: http://www.publicpolicypolling.com/pdf/PPP_Release_National_1119.pdf That second link includes the question wording and order, as well as the crosstabs (if you know what the heck those are). Feel free to take a look at the source to see if you think it has a bias. Also note that Public Policy Polling isn't specifically known for bad polling according to Nate Silver's rankings here: http://www.fivethirtyeight.com/search/label/pollster ratings.
Shouldn't the title of this thread be "Majority of republicans who participated in one particular poll answered (but not necessarily believe) that ACORN stole the election for President Obama"?
If the sample is large enough and representative enough. Theoretically there could be some error where over half of the Republicans that answered the question live near a toxic waste dump or something which skews the results. That is highly unlikely given their previous accuracy, though. Looking through the questions I don't see anything that was particularly biased or anything but straightforward. It looks to be legit. A recent study found that a sizable minority believe that Obama isn't a legitimate president and is secretly trying to completely dismantle the country, but those percentages were in the 20s or 30s I think. This is pretty surprising.
My parents had a dinner party a month or two ago with some old neighbors and the parents of one of my good friends from high school. Consensus from all the eight or so people was that Obama won because of the ACORN scandal. I absolutely, positively believe that the majority of Republicans believe this. Especially if they polled people in the South.
I think some people are just in denial about how extreme the Republican base has become. Why would this poll be surprising when their most popular, high profile figures spew nonsense about government "death panels" and the drones just eat it up like candy.