To be completely honest I cant imagine any one but an enthusiast using tire rack. your average joe probably isn't aware of it and will just go down to there local tire shop.
Never used it, but ive priced out tires on there, and all the times ive checked its no cheaper then using a normal store when you factor in shipping. Frankly I don't want to go through the hassel of ordering it and waiting for shipping and then get the place to schedule me and yada yada yada. Only thing I could see my self using it for is something very specific.
If I were to use it though, I would have it shipped to my home and pick a place to go. would determine where to goby finding some one I know that wont messs up my wheels, and then cost and then location.