As someone who was interested in the Mayans I researched them for a few years, got bored and wandered off to do something else. So from my experience let me tell you something: The Mayans did NOT predict the end of the world. All the archaeologists who studied the Mayan civilisation state this very fact. The Mayans did NOT have any end of the world fables or beliefs. These are the people I choose to listen to, they are the ones who have studied the culture and even point out places where the Mayans have put 'important dates' that fall after the end of this cycle.
Now where did the end of the world stuff come from... well from people who have done NO research into the Mayan culture at all. These people are bathed in the westernised idea of the end of the world, and yes it is a western idea that is not found often outside of Biblical lore. These 'so called experts' latched their pet 'end of the world' theories, of which there are too many to sanely look at these days, onto the calendar to make themselves sound more 'official. You know, to sound as if they where not just talking our of their arse cause now some ancient prophecies are going to be fulfilled! Problem is... no such prophecies exist.
Now if you strip these non-prophecies away from the calendar you do come up with something very interesting. These 'primitives' couldn't even work metal harder then gold but they did some very, VERY, accurate calculations. Through simple observations of the world around them, and a stick in the ground, they managed to map the skies to such a degree that would be thousands of years before modern day tools allowed us to do the same.
The long calendar is much more accurate then the one we use today, which we readjust every four years and still is slowly slipping out of alignment. It pin points numerous astrological events so accurately they can be plotted over the course of tens of thousands of years to the very second. This includes what we now call a galactic alignment, something modern culture only calculated using very high precision instruments, which happens once every 26000 years.
That is why the date was chosen as the start/stop point... no end of the world, just a very intelligent mind worked out when the stars will make a complete cycle around the sky and pin pointing when that date would be in the future.
So what did the Mayans suggest we do on December 2012? CELEBRATE!
PS: For those who say to use google. I have to point out these days it is like sifting chafe for a grain of truth. Particularly when it comes to end of the world theories. There are so many out there your head will, figuratively, explode if you try and read them all. I bet he came here because we are NOT like the people who irrationally believe in the end of the world and hoped he could get some solid answers from someone who looked at the theories and laughed at them.