I'm a firm car addict. Even when I've stayed onsite, I drive everywhere. We just don't care for the Disney transportation with the exception of the monorail. I like to come and go on my own schedule and not have to wait for buses or crowd in with everyone else. I also like to have the option of going from park to park, or visit a hotel, or go somewhere offsite. For example, if we're at MK and decide we want to head over to MGM for a while, I find it easier to do so by car. One final reason is that we're pretty anal about seat belts and car seats which the buses obviously don't have. We just feel more comfortable and safer in our own vehicle.
Steve