I've added USPS shipping.
I had to update the form elements on the checkout page. I had to update the framework builder includes to the latest version, and I had to add code to the confirm_cart.php and pp_confirm.php page.
You will need to make sure you are setting a weight for all of your cart items.
You also have to set the correct origin zip code on line 100 of confirm_cart.php and line 87 of pp_confirm.php.