And what about me that i born the 5th october 1582?
You compensate for your loss by moving your birthday forward one day every leap year.
(This has already enabled me to move my birthday from 18th Nov to 3rd Nov .... you stand to gain considerably more :-)
According to our codebase, it's mythical. An expiry date was set one year in the future, and the code used the obviously correct solution:
my @expiry_date = ($current_year + 1, $current_month, $current_day);
This date eventually makes it's way into a big, ugly C# app that doesn't like mythical dates or providing useful error messages. According to our source control, that line has been there for 6 years. According to our issue tracker, it caused a problem 4 years ago that couldn't be replicated, and was resolved after 2 days by re-running the script. The problem happened again recently...
Feb 29th is a myth for sure! Have a look at the following article (unfortunately in german) as a proof: trouble at the airport. At the airport in Düsseldorf the baggage could not be processed, as the software didn't consider February 29th to be a valid day.