Its just the end of their Baktun long count calender. If their civilisation lasted, they would of calculated another long count calender long before 21/12/2012. No where in mayan culture describes an end time, apart from their usual cultural one, but its something that doesn't dominate their culture, unlike ours
SIDE NOTE: Mayan creation myth speaks of a god that creates three worlds, however only one is deemed fit for mankind. Others die/fade out. Current geological surveys of Mars and Venus has given indications that they where very much like earth a long time ago. with a temperate climate, and oxygen/nitrogen atmosphere. Mars's core cooled down and lost its atmosphere due to the small size of the planet and Venus overheated with greenhouse gases.
One thing does happen on that date is that our solar system/sun/combination (I forget which) will be in perfect galactic allignment, and then proceed either to the upper or lower part of the galactic hemisphere (I forget which, again). However this is a clockwork action that happens every so often. What is fasinating is that this 'galactic allignment' happens the end of their baktun calender. Mayans are well known astronomers and astrologists, and I find it compelling that their end of the long count calender happens to coincide with this galactic allignment. However, as a scientist myself, I find it hard to put scientfic creedence into astrology, however my times in research and study has led me to believe that astrology has very coincidential observations. And things do work like clockwork in the universe (only account for changes that can be observed in a timeframe of millions of years, not in the small amount of time we observe/have observed).
Sorry, completely off topic. However I am interested in this, some of what I said is opinion based on observations and fact. I'm sorry I haven't cited, i'm really hung over. Can do upon request.
Anyway, baaack to topic. Most likely Christmas shopping, knee deep in studying, and spending the day like any other friday!