public opinion polls

Since May's general Election, there's one question I've been asked again and again - how did the polls get it so wrong that an apparent photo finish was actually a Conservative outright majority, an outcome that some forecasters had given a zero chance of happening?
One of the problems with the current election campaign, apart from it being the most sanitised on record, is the reporting about it. National media is fixated on the opinion polls, and the miniscule movements that have occurred during the campaign, and the impact these will have on the overall result.
Ten years on, we meet to ask 'was it worth it?' Presumably not for the many hundreds of thousands of Iraqi civilians killed in the conflict. The figures may vary (Iraq Body Count put the number at around 120,000 while the Lancet counted upwards of 600,000) but the story is one of devastation nonetheless.