FlyingKiwi - if the ailerons are rigged right and the aircraft tends to turn to one side, the recommended solution (by Piper) is to have the flap lowered slightly (by operating rod adjustment) to bring the wing back up. Might be worth chatting to the AMO the next time the aircraft's in on check.
Sorry about the slight drift.
The rudder trim really is a poor design on the PA28; the rigging also affects nosewheel steering if my memory serves right.