As of 2014, the significance of March 14, 2015 is that when it is written out as 3/14/15, it represents the first five digits of pi, which is 3.1415. At 9:26:53, the written numbers are the first 10 digits of pi, which is 3.141592653. This sequence occurs once every century.
A non-binding resolution was passed by the U.S. House of Representatives in 2009 to make March 14 National Pi Day. Common ways to celebrate include eating and throwing pie. Some schools have pi memorization contests. As of 2014, the most places of pi memorized is 67,890; this record is held by Chao Lu of China.