For all the people that think it's dumb to put the parking brake on with an automatic, you are wrong.
Every single automatic transmission equipped vehicle I've seen, the owner's manual suggests you use it every time you park. The parking pawl on an automatic is not really designed to hold the weight of the vehicle, it's just there in case. A manual transmission vehicle won't roll if it's in gear and parked, but you still use the parking brake.
If you don't believe me find a picture of how the parking pawl looks and tell me you trust it to hold your vehicle on a hill. I've driven heavy duty trucks with automatics (think f-550) and they don't even have park on the gear selector since it wouldn't be able to hold the truck anyways. They only have a normal parking brake.