I think an acre or less may be a good cut off point. I didn't realize that most ponds owned by Forum members would be under an acre.
Well most of us are serfs with limited moohlah.
All kidding aside I perfer a smaller pond for intense management. The things I could do with two or three more 1/3 acre ponds! Heck even Grand Poobah Lusk has several small ponds!