Dustin, we often handle this, in the cases where personal information is required for checkout, by requiring the user to be logged in with a full user profile of data before they can load the checkout pages. In this way, before they move to checkout, we catch them with standard DNN pages and modules/forms where we get that data from them. We've gone as far as disabling the "add to cart" buttons too in situations where an incomplete user profile of data means that they should not complete checkout.