That isn't actually relevant. The Mayan calendar that is ending (and leading some people to believe the world is ending, which is stupid) is a purely mathematical calendar that is just based off of their modified base 20 counting system. All that happens on 12/21/12 is that we're coming to the end of one of those 144,000 day counting periods. It has nothing to do with how long it takes the earth to orbit the sun (they had a separate solar calendar for that), so leap days aren't a factor.
Thinking that the world is ending because the number system is starting over is kind of like thinking that your car is going to explode when it's miles go from 99,999 back to 0 (if your car only went to 100k).