Don't forget the group who believes that the world as we know it will change. Its easily possible that out of fear somebody screws up horribly in 2012 which then sets of a chain reactions leading to a major catastrophe. It is also easily possible that a collection of events could happen simultaneously which, even though these events are meaningless on their own, stack up to cause something meaningful to happen.
I.E. the earth's magnetic field being weakened while the sun is at a solar maximum might end up with a large solar flare being shot off right at the Earth. With a weakened magnetic field it could potentially punch right through causing damage to the world's electrical grid.
Yes, I know how slim the chances are of such an event happening. You don't need to comment on that.