I was wondering if anyone could tell me what the ideal length is for an American Smooth ballgown. Should the dress touch the top of my shoe in the back? Should it be mid-calf? Thanks for any suggestions.

hmmmm, "ideal length" differs for many.
Some things to consider, your feet/shoes should clearly be seen by the judges - although while moving or dipping or, etc., your dress may dip down a bit and cover your shoes. Another - how comfortable are you dancing in the dress? Some people catch their dresses with the heels while moving-and would simply prefer not to fall or have anything that would increase the chances of slipping on the floor (i.e., longer than needed dress), others want to insure that they won't so they go shorter. Practice in the dress with the shoes you will wear and you'll find out. Many dresses can be hemmed/shortened or altered in some format. For me? I prefer that the hem of my dresses falls slightly above my ankle bone.

Good advice. I was thinking of keeping it right around my ankle bone.
Thanks.