The census stuff is pretty accurate, and the problem is that when Ecommerce was ported the porters didn't use us-zipcodes et al. So a change to use the standard tables would be very useful. I updated us-zipcodes for 5.0 so the data should be as accurate as can be for free. If someone wants to donate the USPS version which cost $$$ I will be happy to add it to us-zipcodes.
