All endings of the world are rumors, remember the turn of the Millenium? Everyone thought they were going to die. I don't know much about it, but I think this particular "dooms day" is about the Mayan culture; something about their old ability to read the stars, and it being lined up on their calender that in December of 2012 the world will end. Anyway, I guess if you believe in it, then start panicking, but personally I think it's just another rumor.
Just more crazy "the sky is falling" stuff.