Q: By "dates" I mean July 22 / April 4 / etc. Leap days cannot be used as the least common date since it is a given that leap day birthdays are the rarest.
A: For some reason, after Feb. 29, May 22 is the least common birthday. Not sure why. WikiAnswers says the most common birthday is Oct. 5. Possibly as the result of people "hooking up" on New Year's Eve? These are the results of a survey of U.S. Americans.