Now that presidential election is over, people can actually compare the performance of various public opinion polls that were used to gauge this election. The New York Times compared 23 such polls in their article. The famous Gallup poll ranked last among the 23. In addition, internet based Google Consumer Survey actually ranked second in that list.
Almost half a century ago, a novel named "Franchise" depicted a futuristic world where computer estimated public opinion polls can be so accurate such that the entire presidential election can be decided purely based on computer polls and the actual voting become obsolete. Many Asimov sci-fi enthusiasts may remember this story. Yet the story was set in 2008, and we are nowhere close to that kind of polling, 4 years past that projected era.