Yeah, I use a heater. When it's 30° and your out driving, it feels pretty damn good! The wife's only request was a heater. Was I to say NO!
We/I don't feel any engine compartment heat that others have said come into the cockpit when its not in use. I have a F5 car and don't know how this effects other cars out there.
My vote is, if you live in the desert and only drive in the summer, you don't need a heater. However, if you plan on driving around the state (Snakes to the Lake coming up), you better plan on a heater or very warm, insulated and maybe battery powered heat clothing to wear, or you will be miserable.
jm$.02