It would be nice if it were the date for the “technological singularity”.
In reality the Mayan calendar exists as many interlocking cycles, indicating eras of human and spiritual change/evolution/growth/whatever. Where they used what happened in a past cycle (or combination of cycles), to predict the future, the will of the gods and the spiritworld in general. and while they believed in strong influences of the spiritual on the physical, the calender is not about the Earth in itself.
According to what I heard from a south or Middle American who claimed his people descended from one of those Aztec or Mayan cultures, I can’t remember him, anyway:
The end of the this long cycle at 21 December 2012 marks the end of the old structures of those cycles humans have been living in for so long and will be the beginning of openness, where secrets will be revealed.
So it’s not the end of the physical world, but of the current spiritual one.
Ever since I heard this I always wondered if what they were referring to is the growth of the Internet, with smaller, more integrated electronics, internetphones…