Do you go parallel to the ground or ass to grass?

I bought Arnold's Bodybuilding Encyclopedia last night and he advocates a full range of motion, even on squats.

What do you do?

I do parallel personally because that's how I was taught. Now that I'm close to squatting my weight, I don't really want to bring my ass lower because I'd have to put on less weight on the bar...even though it'd be a better pump. Yeah I'm guilty of worrying about quantity and not quality

Anyway just curious as to what you guys do.