I would have to say however, that being without a car would be extremely difficult in Alpharetta proper - due to the traffic situation. There are areas closer to Atlanta that are more conducive to this lifestyle. Atlantic Station is a great example of residential and business coming together. Townhomes, lofts, and apartments are right within walking distance from each other.
You've got to check it out to appreciate it!
That being said, once they added the marta train it made it infinitely easier to get to downtown if planned right. Most people COULD get around in Atlanta Proper without a car, but it would be difficult. In Alpharetta, it just wouldn't be plausible.