The calendar was completely refined and finished. It had 360 days, and a five day period at the end of the year that was supposedly when the spirits wandered between the worlds (Middleworld, the world we live in, Xibalba (she-balba) and the heavens (I forget the name, possibly Itzamna, has he was like the big god). All are connected as part of the world tree (called Chahk, I think, the name of the rain god).
The calendar was separated into b'aktuns, k'atuns, and a few others I can't remember (this from the top of my head). It's basically based around the number eight. A b'aktun was something like 400 years, and I think four of those make a k'atun. As the b'aktun progresses, the calendar goes round day by day (each day even has a name, and they believed the day you were born on denotes your personality). I think they calculated that they thought the beginning of the world was like 3,817 years ago? Something like that. Anyway, it's gone round since a long while ago, and this year it reaches the "end" of the circle. And what does it do? It starts again, like most circles.
Mayans believed in no way the world was going to end. Some day, maybe, if they displeased the gods (in their creation story, they'd tried many times to create life properly, and kept murdering their creations in brutal ways), they thought it might end, but there are still inscriptions in temples of them celebrating someone's birthday hundreds of years in the future (after 2012).
Edit; I found a picture of the world tree. :D.
http://3.bp.blogspot.com/_gPp74AFBiv...ons%5B1%5D.jpg
Edit #2; this Wikipedia page can teach you better than my memory can:
http://en.m.wikipedia.org/wiki/Maya_calendar#_
It explains the year cycles and the calendar itself more, which I was vague on / got wrong.
I still think I went pretty well off the top of my head though lol
