Programmer's Day
Programmer's Day — official programmer holiday in Russia, celebrated on 256-th day of the year. The number 256 (28) was chosen due to the fact, that it's the most big power of two less then 365 (days in the year).
On the leap year it's celebrated on September 12th (September 13th otherwise).
Starting from September 11th, 2009, Programmer's Day is an official holiday in Russia, still it's widely celebrated by programmers in other countries, being effectively international.