This looks like a pretty terrible movie. Let's be honest, there's going to be 25 to 30 minutes of widescreen destruction and then a plot and dialogue so formulaic as to be procedurally generated.
This flick, by comparison, looks totally awesome sweet, but I attribute that mainly to the largely bongo-oriented soundtrack.
Here's the thing: 21st December 2012 represents a fairly major digit rollover in the Mesoamerican Long Count calendar. It's the Mayan Y2K. 220.127.116.11.19 will roll over to 18.104.22.168.0. That is all.
We don't use Mayan software. We don't use it because the original engineers who created that software were wiped out five hundred years ago and you can't get the support contracts anymore. Even if we did all use Maya OS, we'd just patch all the vulnerable systems and it would be a non-event like Y2K was. And even if we didn't do that, the failure of every computer on Earth would not bring about the fall of human civilisation because well over fifty percent of human civilisation still doesn't rely on computers.
The reason I'm talking about computing is because this is the only way that a major calendar digit rollover could possibly harm anyone or anything.
This is because dates are not real.
The real world does not care what year it is. Do you have a desk calendar which ends on 31st December 2010? OH NO IT'S THE END OF THE WORLD. Dates and times are almost entirely arbitrary constructs, used by humans to provide a sensible, internally consistent reference framework for the recording of past events and the planning of future ones. In theory, all events past and future could be described with reference to the present time; "I was born 25 years ago" rather than "I was born in 1983". But this makes it impossible to record time-sensitive data in a static format, such as written text (a year from now, "I was born 25 years ago" will be incorrect), so instead we choose an arbitrary universally accepted reference point to start counting time from, an "epoch", and then when I say "1983" I mean "1,983 years after the epoch" and you understand that to be "1,983 years after the epoch" and we are talking about the same year because we have the same definition of "the epoch".
By choosing a different epoch or a different calendar system, any day you like can be 6/6/6 or the year 10000 or whatever number of significance you wish to generate. What makes one epoch more significant than another? The fact that a lot of people use it? There are millions of people who use calendars other than the Common Era. As for the number of people still using the Mesoamerican Long Count calendar, that is almost exactly zero. A friend of mine created a decimal calendar which counts backwards. To what? Nobody cares.
It's superstition, like being frightened of the number 13. It's numerology, it's a distraction, and it's passing the responsibility. If you want the Earth to be destroyed, you can't just sit at home tabulating thousand-year-old religious texts for patterns which aren't there and then sit and wait for the moment when all your stupid graphs cross. The end of the world is not something that happens because cosmic forces aligned and decided it was time for the world to end, and even if it was, figuring this fact out in advance would not hasten it.