I had the privilege of studying with an excellent teacher in middle school for Life Science and later in Physical Science and his equally excellent wife who taught Earth Science. One of the pearl of wisdom they imparted was the use of the metric system or Système International d'Unités. I still remember the basic conversion table (0°C = 32°F, 10°C = 50°F, 20°C = 68°F, 30°C = 86°F, 40°C = 104°F) to this day.
The project that I am finishing up at work uses a DCS and it has a mish-mash of English and metric units creating utter confusion. It is times like this when I wonder when the U.S. will ever formally adopt the metric system. Of course, foreigners do not realize the havoc it would cost as well as sheer amount of time and money. However, if you plan on adopting the system at some point, I believe the sooner the better -- slow introduction only serves to delay it or postpone it more. It may never officially be adopted in the U.S.
My wife and I recently were in a production of 1776 and on the wall in Congress (on the stage that is) one of the prop pieces was a old fashioned barometer. I noticed that the units were metric based and it made me wonder when the metric system was introduced (the audience couldn't see it that closely though). It seems according to wikipedia the metric system was first described by John Wilkins and that Benjamin Franklin may have been involved in communicating the system from England to France. So, for the purposes of the musical production and since Benjamin Franklin is a principal character in the musical, we'll just attribute the metric barometer as one more thing Congress could not agree on.
This brings me to the date format. I am a big fan of the ISO 8601 year-month-day format. Developers need to use it where ever possible -- many use it incidentally through web services without knowing it. I try to make sure to use it everywhere, including log files and the UI (unless the customer requests otherwise) and I recommend you do the same.