I always store them as YYYYMMDD HH:MM:SS.MS (Or without time if Date), I should use UTC and have at a couple of places, but I think it is business dependent, although maybe it shouldn't be in this day and age.

Either way, the way you want to display the date is then entirely up to you.

It does amuse me though that Americans are the only ones to use the weird MMDDYYYY format, I say kill that with fire..