Was it Nostradamus who said 2012?? I wouldn't trust him anyway lol, his quatrains are sooooo vague you can apply them to ANYTHING, especially with the benefit of hindsight (eg, applying something like 'birds and fire' to 9/11, after it's happened, kwim?).
The Mayan Calendar ends sometime in December 2012, apparently they did their calendars in cycles according to the planets/stars - and that date is when another 'cycle' ends, and all the planets in our solar system are apparently lined up. I don't know what that means as far as the 'end of the world', but I personally am inclined to think it means little - were the Mayans expected to write their calendar up until, say, the year 8439, and then people living in that time would be freaking out thinking the world was going to end, kwim?

My husband has recently become morbidly obsessed with the 2012 prophecy, so I'm hearing bucketloads (and being subjected to endless docos on the History and Nat Geo channels lol) about it from him. Personally, I don't like to think about it too much - it's confusing and I'd rather not think about the possibility of the world ending