on steep shit you'll end up getting more hangup in your tail edge once you initiate your turn, and that can really put a damper on your all mountain skiing ability, which sucks.
I would imagine you would notice more of a difference with centermounted skis all mountain rather than in the park. My personal opinion is I think it's retarded to center mount. The ski is designed with a certain mountain position to the freakin millimeter.......why mess up the cut of the ski by center mounting.