Yes, it's Square Root Day, a holiday that only comes along every few years. Today is 3/3/09, which as everyone knows, 3 is the square root of 9. (And I did that without a calculator. I was very good in math in school.)
The last Square Root Day was February 2, 2004, or 2/2/04. And the next one won't be for another seven years, on April 4, 2016.
So celebrate while you can, because the holiday doesn't come around that often, as after that it doesn't happen until 2025, 2036 and 2049.
I would have done "Square Root Day" as a Trivia special category tonight if I had realized it sooner. Oh well, there's always 2016.