I saw a show where they interviewed a few people about this world ending thing. The mayan cultural guy who was a descendant was the most interesting. he said that other writings refered to astronomical events expected in 4000 something. So the calendar was just a calendar.
His next point was that he had a calendar hanging behind his desk that ended on dec 31 2011. And that he didn't expect the world to end then, just the usefulness of the calendar.
of course, those in the know have the truth - On dec 21 there will be a "rapture" for all baseball cards made between 1986 and 1993. They will be entirely removed from the earth and the resulting loss of mass will cause the earth to leave it's orbit thus ending life as we know it. (So make sure to put them all outdoors, lest you require roof repairs)
Steve B