I will be doing Atkins when we go to WDW in February, also, so this interests me as well. I remember reading some time ago on the WISH board that Ray Sharpton spoke with the chef at O'Hana's about staying low carb while eating there and it was more difficult than he anticipated. Apparently, they use a lot of sauces and so forth that contain large amounts of sugar, and so he had to have his meats specially cooked without those added carbs. At any rate, he was successful at eating low carb while at Disney, so there is hope for the rest of us!
I have also read that there are frozen juice bars in the ice cream carts that are about 8 carbs apiece (I think I read that on Deb Wills' site). You have to be careful about the sugar free ice cream because it still has more carbs than lots of Atkins dieters would want to consume (probably because of the milk).
The turkey legs that someone mentioned are wonderful. The last time I went to WDW, I ended up eating way more carbs than I should have and felt really yucky before I came home. That's why I want to stick to Atkins on our February trip - I will need all my energy for the walking!