Ask HN: How do you treat your users that are born on Feb 29th?

In the case of common year, when it is appropriate to send a greetings message? I guess the most common approach is to do it on 28th, but in some cultures it is considered a bad sign to celebrate the birthday a before the actual day. Viewing from the programmer perspective it is now obvious that an implementation which compares the current day with user birthday date and performs some sort of action is not a very wise one.