Don't do what I did. I canceled before my car came in. If I had to do it over again, I would at least wait until the car hit the showroom and THEN tell them. This way your local smart center gets an extra car to go to someone on THEIR orphan list.
If you cancel now, your order is canceled and your car will never be built. Someone will take your orphan at the end of next year if you don't want it. Besides, with a DDE of Oct-Dec, you could still get a 2010.
Speaking from experience, I would wait it out if i were you.