Tasker can do that but it's a bear to learn - I bought it when you had 24 hrs to get a refund and realized it was more then I wanted to tackle at the time. Others who have spent the time to play with it swear by it. Since there are no Car Dock Magnets to tell the phone when it's in the car, like the Droid, you would still have to launch something to initiate the tasker event, but I guess 1 button is better than 3.
I just use the Power Widget when I’m getting in the car. When I was running Sense I had it on the second screen, 1 flick, and press BT on GPS on and whatever else off. CM7 has it in the task bar.