How will the end begin?

The end is near. At least that's what the doomsday predictions from Nostradamus, the Book of Revelation, the Mayan "long count" calendar and others would have us believe. Many unsettling forecasts of global destruction even pinpoint the year: 2012. How worried should we be? If these prophecies are accurate and inevitable, is there any way to avoid or at least postpone them from coming true?