My wife arrives one hour early for domestic flights and has yet to miss one (she travels as part of her work). I even in my anal-retentiveness about flights rarely arrive more than an hour and a half early. So there is a good amount of time you are leaving on the table that you could reclaim. I hope this series of comments will help you waste less time and money driving.
Well, I fly into the US from outside. That entails rechecking all baggage and going through a second security line. There are less airports you can fly into now from the outside and all of those I've been to so far have huge lines at the security. We now schedule in 4 hours between that initial connection and we've still almost missed the connecting flight a few times.
What all does that involve, and how was it different pre-9/11? You can't pack a bunch of fluids in your carry-on, so you have to get little travel things - that's not worth 7 extra hours.
It's not a straight x/y calculation. For me, going through security usually takes between 40 minutes to a couple of hours depending on the air port. But the experience is so awful that I dread it for hours ahead of time and am infuriated by it for hours afterwards. I don't like driving long distances but at least I can avoid some of the stress.