Of course you only say it that way in America.

Today is the Thirteenth of May, not May 13.

I prefer dd/mm/yyyy to yyyy/mm/dd though, just to keep what is usually the most important information at the front.

I like YYYY-MM-DD for two reasons:

1) Sorting the string representations sorts in time order.

2) It eliminates ambiguity almost completely, because extremely few places use YYYY-DD-MM. The ambiguity of most ##/##/## dates is irritating.

I prefer how we did it in the military: 13MAY2011. mysql: %d%b%Y

No ambiguity, easy to parse and 3-letter month is natural delimiter between day and year numbers.

dd-mm-yyyy can easily be confused with mm-dd-yyyy. The only format that is obvious is yyyy-mm-dd.

Until somebody starts using yyyy-dd-mm and screws everything up.

Besides, often when you write dates you leave the year off entirely.