In Regional Settings, Windows allows you to set your Language(Country), Number, Currency, Time and Date preferences.
My Regional setting is English (Canadian) and my Windows Date setting is YYYY-MM-DD.  (In Canada we have an official standard 
YYYY-MM-DD, and the standard practice based on tradition which is DD/MM/YY.)

My OOo Default is set to English(Canada), but my spreadsheets date default is DD/MM/YY. It does not refer to my Windows settings.

If I format the cells for YYYY-MM-DD, they will display as desired, but editing is a pain since the edit format is different than in the reference 
document.  If I and/or my subordinates are thinking clearly we can get the edits done correctly but it is more difficult than it should be. It is 
also necessary to format the cells first, then enter the dates in the formatted cells in the full YYYY-MM-DD format.  Dates entered as 
YYYY-MM-DD before formatting the cell are entered as text. Dates entered YY-MM-DD are interpreted as if they had been entered in 
DD-MM-YY format, reversing the day and year.

IMHO this issue is closely related to issue 5556 tagged as resolved invalid.  I agree that you need to be able to edit the underlying data, but 
that underlying data should be displayed in the required default format.

OOo should either pick up all the Windows settings or should (preferrably) allow full customization of defaults in Options, so that the default 
formats used for editing correspond to the required regional standard.  In many cases people have to work on documents complying with many 
regional standards, so setting the defaults in OOo and saving them with the document would be the most general solution.