Let me start by saying that using mm-dd-yyyy is just plain wrong. No really it just doesn’t make any sense to me. Neither does it make any sense to most people world-over if you go my the date-format map up at http://en.wikipedia.org/wiki/File:Date_upd1.PNG

If one uses dd-mm-yyyy it makes sense because it’s in decreasing order of granularity (kind of LSB first). yyyy-mm-dd makes ever more sense because

  1. It’s in decreasing order of granularity
  2. Natural ordering in many ways like telephone numbers (country-code, area-code, local-code, number) or IP address
  3. String sorting automatically sorts by that date. E.g. I can easily have folders/files named in this order and DIR lists them nicely sorted out (yea I know I can sort by date/time as well).

d:\MyStuff\Personal\Pictures>dir 2010*
Volume in drive D is Data
Volume Serial Number is 3657-F386

Directory of d:\MyStuff\Personal\Pictures

06/17/2010  01:06 PM    <DIR>          2010_0501
06/17/2010  01:07 PM    <DIR>          2010_0504
06/17/2010  01:16 PM    <DIR>          2010_0508
06/17/2010  01:20 PM    <DIR>          2010_0509
06/17/2010  01:24 PM    <DIR>          2010_0515
06/17/2010  01:29 PM    <DIR>          2010_0517
06/17/2010  01:30 PM    <DIR>          2010_0523
06/17/2010  01:33 PM    <DIR>          2010_0528
06/17/2010  01:37 PM    <DIR>          2010_0529
06/17/2010  01:43 PM    <DIR>          2010_0605
06/17/2010  01:47 PM    <DIR>          2010_0606
06/21/2010  08:40 PM    <DIR>          2010_0616
06/28/2010  10:33 PM    <DIR>          2010_0619
               0 File(s)              0 bytes
              13 Dir(s)  55,925,829,632 bytes free

But I just cannot fathom why would anyone use mm/dd/yyyy. In what way is that intuitive?