December 21, 2012 is simply the end of the "long cycle" of the Mayan calendar, after which a new "long cycle" starts. Kind of like Saturday is the end of the week, after which on Sunday a new week starts.

If you're into planning, you should start now to plan the business of selling end of the world stuff in 2011.
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Knowing where you're going is NOT the same as knowing how to get there.