As someone with one foot in the business world and one foot in the
scientific world, the most successful date/time standard that I have
ever seen is the julian date standard as used by the astronomical world.
The astronomical world uses exclusively this single standard.  It is
unambiguous, specifying not only date but also time in a single real
number, for anyone on Earth, regardless of time zone and daylight
savings time.

For instance, at this moment, Julian Date:  2451080.257209

Astronomically, JD starts at noon.  However, when the time fractional
part of JD is not used, in non-astronomical applications such as
business applications that have a scientific component, JD is taken to
begin at the local machine's start of day.

To say that JD is yyyyddd or starts sometime in the last century or two
is equivalent to arbitrarily calling Wednesday Monday.  There are so
many calendar systems around the world in use, but only this one
standard that is instantly understood regardless of nationality or
culture or geographic location.

Mel Bartels
http://www.efn.org/~mbartels