This YouTube video
is worth watching. It's put together by conspiracy mongering 9/11 types, but has a redeeming factor to it. Most of the video has a so-called truther quizzing college kids as to what year 9/11 happened. Most of those shown give wrong answers or simply don't know! Even assuming they showed a very skewed sample of those polled, the fact that you could find this many people in an afternoon at an American College who don't know what year 9/11 happened is astonishing.
Factor in the people who are aware of what year the attacks took place, subtract the group that thinks the incompetent Bush Administration masterminded it, take away the contingent that thinks it gave us cart blanche to invade half the world and your left with a terrifyingly small number of rational adults.