I wasn't fast enough on the reply before http://www.gravityhelp.com/forums/topic/modify-qty-portion-of-product-field-to-accept-decimals#post-56299 got closed but the answers did help although I did find something that was odd. I am using Chrome and I turned off HTML5 output and when I use a combination of the Product Field w/ the quantity property disabled, and the Quantity Field tied to that product, I can now enter decimals. However if use the Product Field w/ the quantity property ENABLED you can not use a decimal. Does that seem right?
Also, Rob, since you asked, we use the form as an internal invoice for our commissary kitchen. They ship out lbs of things like tuna salad and the like and not always in nice round lb increments.