Mach_D,
You`re right, I have had an excellent reponse, and I would like to thank everyone for all the helpful replies.
I think I may have mis-represented my instructor a little, however. I am coming to the conclusion that what he meant was "we`re 5 miles from the field after a long flight, so if your foot hurts don`t worry about keeping the ball in the middle. You`re fighting the trim, which is out of whack - once it`s fixed the plane will fly straight. For now, just let it do what it wants." In my ignorance I misunderstood him to mean don`t worry about it EVER, which as so many of you have pointed out, is patent nonsense.
The shock of what I THOUGHT he had said made me forget or doubt everything I thought I knew about aerodynamics and the forces acting on a plane in flight! You have all helped to ease my fears...thank you. (Still planning to do some gliding, though.)
Mach_D, sometimes it feels like I am teaching myself to fly...hour-building for the Commercial!