I can understand if there were any clear benefit to use the old imperial units, but there is none (zero, zilch, nada, other than nationalistic pride) and lots of downsides, so is about time you guys enter the 20 century and make life simpler for everyone.
Metric makes it so easy to get calculations wrong in ways that are hard to detect.
1. write you 'n' with 1.5 humps (a habit from writing cursive) or write your 'm' so that it looks like cursive when you didn't mean cursive, and suddenly a nm is a mm or a mm is a nm and your measurement is off by a factor of a million. In Metric all abbreviations in a given dimension differ by one letter, but in Human measurements they differ by 2 or more.
2. In Human measurements conversions usually require a bit of calculating rather than just decimal moving. A double-check shows clearly and easily whether you're in the right ball-bark. With the Reign of Terror measurements if you miscount on moving the decimal you're not likely to notice (or even bother to try) so you can easily be off by a factor of 10.