What most people don't realize is the Mayan calendar is ... cyclical! When you get to the end, you go back to the beginning. So when the Mayan long-count & galactic day calendars coincide to "end" on Dec 21 2012, it's like New Year's Eve for the next 5126 years. (So we should throw one heck of a party, yes? )
Thalia, just to clarify:
The Mayan calendar didn't have to take into account leap years. It's actually more specific than the Gregorian calendar (that most of the world uses) which has to have leap years. So saying the Mayan calendar was "wrong" because it didn't have leap years is incorrect. It was the people doing the math to calculate the end of the long-count cycle who didn't take into account leap years & the adjustments made to our calendar cycle over time.
Of course, there's also the thought that the original start date of the cycle could have been mis-interpreted, and we may have already passed the into the new cycle ... as much as a decade or possibly even a century ago. Or that it's actually next year or two years away from now. *shrug*
At any rate, I'm sure enough that the world isn't ending just because I have to buy a new calendar. I do that every year anyway.
(Now, world ending because some idiot decides it'd be a grand idea to declare nuclear war - I can see that happening anytime.)