The Mayans were just gonna build a new calendar in 2012. The Aztecs and Incans...not sure why people mention them in relation to 2012. As far as the nearest known date teh world could end...it's in a couple centuries, but being an asteroid threat there's always a huge chance the orbit will be found not to hit the Earth (or deflected).
Pssh, This is bull. God will not blow us up in 2012 people! Wake up and smell the croissants! But, with all the recent earthquakes, oil spills, dumbass liberals, among other things, it may very well end sooner! By our own hand!
I'm pretty sure the world was originally going to end in 2000, according to a lot of people, but I don't remember. Point is, it never did. Even IF it happens, I won't spend the last 2 years of life worrying myself to death about it. xD