It would be so very useful to be able to display a different format to the format used as the actual value.

For example, in the UK we use the display format dd/mm/yy which is how i'd like users to see the date in the box when selected.

But we still use the MySQL date and datetime column data types as-is, and as such it would remove a conversion headache to receive yy-mm-dd from the date picker on a form submission.