We've done the drive twice: once when my kids were 3 and 1, again when they were 6 and 4. Our third trip we flew, but in six weeks we'll be driving again (kids are now 14 and 11).
We are in NJ, and quite frankly the drive isn't that bad. As others have said, plan timely breaks to stretch your legs a bit. Pack water and snacks in the car, and often you can get away with only two meals: breakfast and a late lunch/early supper. The DVD system will certainly help.
For my family, flying was nice but we still rented a car. Despite the Disney transportation system, I hate the waiting and much prefer knowing that my ride is waiting for me. The one incident that cemented that decision was when, on a prior trip where my husband had to take the car to a business meeting, my kids and I had to use the busses to go to Fantasia mini-golf. What normally took us 10 minutes by our own car took 90 minutes by bus. Huge waste of time. Plus, with our own car we have the option of going off Disney property to eat or do other activities.