The Mayan Calendar is no different than any other calendar. It starts with a new year and ends and then starts over again.

What makes the Mayan Calendar so significant is that it not only has a Lunar and Solar Calendar but an "Age" Calendar. Besides showing the observable cycles that take only one year, they were able to calculate a 5 age calendar that ended with the Sun rising parallel to the galactic center. Amazing. Completely amazing. But it's not a doom calendar. After the event the calendar simply starts over again at the first age - a time for replanting, rebuilding which is basically, I believe, a metaphor for "the beginning".

I just don't think the world is going to end on 12/21/2012. It's a celestial event. A marvel in itself, but made even more amazing by an ancient people who were able to calculate an event that only happens once every 26k +/- years. This is what impresses me.