We have four young kids, and the logistics of getting all of us, and our stuff, on/off an airplane sounds very intimidating. The last time we flew to Disney, we only had 3 kids, and it was very challenging, especially since the kids couldn't really be counted on to carry their own suitcases. I also stressed a lot about getting seats together. Oh, and we also ended up doing on of those mad dashes to get to the plane (although we had left WDW 3 hours before our flight), and in the process "lost" my dd (3 at the time) for a short time (probably 30 seconds that felt like 30 hours. We decided then that we weren't ready to fly again until all of the kids were older. Now that we have on more child, there is no way. In addition to the stress, it would cost a minimum of about $1600 to fly.
We drove down last year, and it went much better than expected. We split it up into 2 days (14 hours total driving) and made sure to make a few extra stops, just to run around. I got the kids a small game/toy (all Disney related) for each hour. Luckily, my youngest two took naps, which helped a lot. We have a DVD player in the car, which was a lifesaver.
It went so well that we're driving down to FL in March (not WDW), and are planning to drive for our next trip to the World in January '09. In March, we are also bringing our two dogs with us, so that will be an additional challenge.
Now that my oldest two are more capable of carrying their own suitcases, I am not totally opposed to flying with the kids. I would still worry about the logistics of sitting together. My oldest is autistic, so sitting by strangers would not be an option anyone would want. But right now, the cost is way too much. I did check, but I'd much rather spend that $1200 savings to upgrade to the savannah view at AKL!!!