I hate entering things twice. When I get a form mostly filled out, and something happens to cause me to lose the data, oohh. I hate that.
So entering the city and state on every form is bad too. If you have a correct zip code, you know the city. Then I found this nifty tutorial to auto fill the city from the zip code. Check it out. Smooth.
I decided to look into zip codes a little more.
From Wikipedia.
ZIP codes are a system of postal codes used by the United States Postal Service (USPS) since 1963. The term ZIP, an acronym for Zone Improvement Plan,[1] is properly written in capital letters and was chosen to suggest that the mailtravels more efficiently, and therefore more quickly, when senders use the code in the postal address. The basic format consists of five decimal numerical digits.
Interesting. I pledge to never make anyone fill out a zip code and a city.