xanzacow is correct, our calender at one time didn't even have the year zero. 18.104.22.168. is a doomsday date for the Aztecs and their world. There are many doomsdays from many different tribes.
One doomsday prediction is when nine year old girls having babies - that's already happened.
The 2012 is about astronomical conjuction - that already happened in 2010.
Many sign & omens from all over - the rise & fall of civilizations has happened many times over. I.E the Sphinx is much older than ancient Eqyptians - they kept rebuilding it and restoring it over and over again until now it's has a tiny pharoh's head on a huge body.
I am planning to get a Sarah Palin bumper sticker for 2012 because - hey! the world is supposed to end anyway!