There is an ISO standard (8601) for displaying date/time information, see http://www.iso.org/iso/date_and_time_format. It would be a nice addition to the current format options for Date, Time, and Date&Time fields (Short/Medium/Long) if an ISO-8601 compliant format was available. For example:
Date: YYYY-MM-DD
Time: hh:mm:ss
Date&Time: YYYY-MM-DDThh:mm:ss
Taking it one step further, it would be useful if time zone information could be specified in the Time and Date&Time fields to allow an unambiguous value, for example, the current time could be specified in UTC as
12:58:30Z
2010-02-06T12:58:30Z
or in my local time as
05:58:30-07
2010-02-06T05:58:30-07