The pre-Columbian Maya were smart people. They got a lot of things right. So, if their calendar ends on December 12, 2012, the world must end on that date, right?
I hope you didn't believe that line of reasoning: not only because it's flawed, but also because the Maya calendar doesn't really end on that date. It's sad to think that such a thing is necessary, but NASA has set up a page debunking most of the doomsday theories that are circulating over the web, mostly related to the movie 2012.