Hi folks, just joined up and had a quick read through some of the thread.
Our son Owen is almost 4 and has Menkes disease, despite his disabilities he is a very happy little boy and he is just the light of our lives. We are based in the UK and Owen has just recently been granted a wish from MAW to go to Florida and we are staying at GKTW. I've read so many great things about the place and really cant wait, I think i'm more excited than he is!! We are planning on going in early December as the theme parks will hopefully be quiter then or so i've read, one thing we are not looking forward to though is the 9 hour flight.
I am so glad you are excited!
How cool you guys get to come to the States. 
I love early December - the weather is usually good and the parks relatively empty!
As Owen is confined to his special wheelchair he will be limited as to what he can do, we also have Olivia who will be almost 2.5 years when we travel so really we need to plan whats best for them both. I'm thinking that US would probably be a bit too much for them, not sure if they have much for their age groups and I think the time may be better spent elsewhere. Certainly we will be spending the 3 days around Disney without question, we all adore anything Disney! epsecially Owen. I think they will both really enjoy Seaworld too, is there any possibility we can arrange to have Owen (and Olivia) swim with dolphins there? I think Owen would love this kind of interaction and especially in the water where he can feel much more free than in his chair.
I honestly think you will be surprised at how much he can do. Is he verbal?
Lauren can't stand or walk, but she was able to ride a lot of rides. Many in her wheelchair! We were amazed at how accessible everything was. Some rides we had to pick her up and hold her, but that worked well, too. 
You have several options for Dolphin encounters. The most elaborate (and expensive) option is Discovery Cove - which you can pay to have a whole day of activities including a swim with the Dolphins.
Epcot also has a dolphin excursion, though. The problem you are possibly going to run into is his age - I think you have to be 12 or something before he can get in the water with them.
Lauren's Dolphin Experience
Honestly...the dolphin experience was enough for us for that first trip. It was a very close encounter and something Lauren still talks about!
We are not keen on driving around in America so was wondering about transport, MAW over here told me that they provide shutles to and from the parks and when you want to return to GKTW then you just ring for a shuttle, is this correct?
I second what everyone has said...I totally see that it could be a problem if you are used to driving on the other side of the road? And to be honest...driving around Orlando is not the easiest thing - I tend to get lost and I drive on the "right" side of the road all the time.
You could try the shuttle and then ask for a car later?? Not sure on this one.
If you DO use the shuttle...just be aware that it only heads to Disney at 10 AM - which may seem really late (since everyone on the DIS would tell you have to be at the park at rope drop or you will miss everything...but the GKTW button will help so that you won't have to worry about getting everything done.
And the # of wheelchair spots are sometimes limited - I am sure it depends on which bus the company sends.
All in all really looking forward to it, after a week in
Disneyland Paris 10 weeks before we go it should put us right in the mood!