Today on Google.com is a special logo, aka Doodle, for it being a Leap Year. Today, February 29th is a Leap Day, where we add another day to the calendar.
Google explained "the 29th of February only happens every four years." This is to keep our calendar in sync with the rotation of the Earth around the sun. Without Leap Day, we'd be out of sync by about six hours per year.
Google added, "Leap Day happens every four years unless that year is divisible by 100. If you were around in 1900, you would have missed out on the magic of February 29."
The Bing home page is pretty cool also:
Forum discussion at Google+.