A while ago on this site we discussed "the golden mean" which is a concept that states something like: this is a universal dimension, repeated in nature, that we seem to be drawn to and feel comfortable with.
The shape is used close to, and used in things like 8x10 dimensions, credit cards/id cards, magazines, newspapers, you name it.
However TV screens are square, or were, and we have gotten use to that.
Personally, although I shoot with a 6x6 I have almost never printed a square print. Even though it works great for certain things.
Cheryl shoots and prints square almost exclusively, so her input would add to the discussion.