In a sense i dont think its gonna happen, cuz u know all these weird theories like tat Y2k and stuff like that. In another sense, MANY different cultures all point out to 2012 being the end of the world. And even the Mayans had the Long Count calendar ending on December 21 2012. So i really dont know what to believe. I mean i hope it doesnt happen i but think SOMETHING will happen, maybe not the end of the world but something. Because the magnetic poles of the Earth will shift since it is switching sides in the Galaxy (going on the other side of the disc). And that happens every 25600 years and that is on 2012. But if it will have a major effect on our planet? I dont know. It has happend before as our planet is 4.6 billion years old and not all of the animals are extinct. So we just have to wait and see.
Edit: Ya and it doesnt have to be something as crazy as like some of the theories, but the world can be ended by war, Global warming, magnetic pole shift causing serious weather catastrophes... etc..