People tend to write date code themselves, no matter how many times we tell them not to. There have been leap year bugs in everything from Zune to Windows Phon

People tend to write date code themselves, no matter how many times we tell them not to. There have been leap year bugs in everything from Zune to Windows Phone 8 to iPhone/iOS. This, in spite of legions of CS professors trying to get it into people's heads that they should be using libraries (once, of course, they have verified that said library is accurate).