"Why's that?" I hear you ask.
Well, it's because 14 March is 3/14 (in the confusing, American-favoured month/day date format), and 3, 1 and 4 are the three most significant digits of π in the decimal form. That's why.
To find out more about Pi Day, follow this link. And to mark Pi Day, why not buy yourself a T-shirt? :-)
Larry Shaw - a.k.a. the Prince of Pi - the organiser of the very first Pi Day. What a guy!
(At least now we know the answer to the question, "Who ate all the Pi?")