Gallup, etc. are an important wheel in the opinion-shaping business (propaganda) for the establishment.
Yes, surveys can be very accurate, but that accuracy can only be verified by outsiders once in a while, such as comparing their projection to actual vote counting after elections or referenda. This earned credibility can then be leveraged over the rest of the time, where they can basically make up numbers out of thin air. The one paying for the survey, still gets the correct numbers and react accordingly, akin to two sets of books.
Can this be proven for yesterday's poll? Not without a whistleblower, but...
Perhaps the best known example:
http://www.mises.org/misesreview_detail.aspx?control=122&sortorder=issue
The polls that showed American support for violations of neutrality were rigged by British agents. "British intelligence had `penetrated' the Gallup organization.... British intelligence officer David Ogilvy later wrote about his days at Gallup: `I could not have had a better boss than Dr. Gallup. His confidence in me was such that I do not recall his ever reading any of the reports I wrote in his name'" (p. 75). By careful manipulation of the questions asked, results could be contrived to order. "In 1940 and 1941, BSC [British Security Coordination] rigged a series of polls...to project the notion that the members of prominent organizations were pro-British, avidly in favor of intervention, and intensely antagonistic toward America First"
I contend that the Ron Paul Revolution is viewed by the 'other side' as at least as a serious a threat to their interests as the situation described above, because this time, they not only risk to lose "the enforcer" of their global protection racket, but the Fed (and all that flows from it) as well.
The 'scientific' polls will reflect the wishes of the plutocracy - lagging about 10-20 points behind reality - until shortly before November08 - then Dr. Paul becomes President Paul...