The product weight is not displayed to the user anywhere in the front end product catalog or checkout. The only area in the cart that the product weight unit of measure (ounces vs pounds) is used is the real time shipping calculators UPS, USPS, FedEx or CanadaPost in the checkout. The label "Ounces" on the add products screen could be changed to grams or anything you like and unless you are using the real time shipping calculator in the cart there are no implications.
-Scott