These polls are inaccurate even if the data is not faked. If you are doing the poll for Fox News you ask "Are you pleased with they way Obama is completing ALL of his campaign promises?" if you are doing the poll for MSNBC you ask "Given the state of the country Obama inherited are you pleased with his progress so far?"
Not true. If you had been following Nate Silver's site http://fivethirtyeight.com/ in the lead up to the presidential election, you'd have gotten VERY accurate poll results.
One thing that has always bugged me is how can two polls give different results to effectively identical questions and both claim to have "plus or minus 3%" (or whatever) margin of error, when their results have substantially larger differences than that?
Keep in mind that defining a representative sample is also fraught with differences. How you you determine if someone is a likely voter (are they registered? did they vote last time? other or some combination of the above?), for example, or ensure what you believe is a representative sample of different ethnicities?
Because a sample of 200 - 1200 is used and multiplied out to represent the population as a whole, tweaks in those definitions can lead to different results for the same questions.
I definitely second the www.fivethirtyeight.com tips, as well as www.electoral-vote.com for regular outside analysis of polls and discussion of methodological differences among the various polling places.
