keith smith: unless I'm missing something the tail feathers are generally generating lift in a downward direction, resisting the inherent tendancy of the wing to pitch nose down, thus I would imagine the low thrustline 'unloading' the elevator might have some efficiency benefits.. whether it's significant is another matter.
However, in reality the thrustline / engine configuration has far more to do with the practicality of where to hang the things - high wings are more of a pain to engineer (a'la 146), and pod mounted engines seem to be the solution vs wing root/back end of fuselage (bending moments etc). the pitch couple is an (undesirable?) side effect that has to be lived with.
ISTR seeing something somewhere out there with the pod mount flipped upside down putting the engine over the wing... along with a bunch of marketing waffle that I can't remember about how much better that config was. Doesn't seem to have caught on however..