If you take a ski that has a 4mm difference in width between the tip and tail, mount it dead-center, and can tell a difference skiing backwards or forwards, well then, you:
1) Are the best skier of all time, and should be a product tester for every company out there charging $50,000 a minute for your time....
or
2) Should be involved in the space prgram.
Either way, it's more than likely you won't notice a difference...