When me and DH are there with the car, we use it to get around, especially on non-park "resort" hopping days, because buses don't go resort to resort, which kind of surprises me since the resorts are so themed one could make a day (and do) just exploring resorts.
When I am there with a girlfriend, in which case we fly, we spoil ourselves and have a car service pick us up at the airport, do a grocery stop and drop us off directly at our resort, and usually use cabs to go resort to resort, and buses/boats/monorail to go to the parks.