Did you know that 2012 is a Leap Year?
It has to do with keeping the calendar year and the astronomical year harmonious (ie, synchronized).
If you cannot remember whether a particular year is a "common" year or a "Leap Year," (and you are decent at math), just divide the year by four. If the result is a whole number, and not a fraction, it is a Leap Year. For example, 2012 divided by 4 = 53.
One funny bit of folklore contends that these extra-day years are the only times where women could propose to men. It was known as "The Ladies' Privilege."
When I was a kid, I knew a boy whose birthday was on February 29th. We thought it was so hilarious that when we were 12, he was only 3 (ha-ha, right?).
There is a cute term for those born on the 29th of February...