Insulating the doors

I have put off doing this, and maybe I never will, but I am considering taking my side door off to add bracing for latch and insulating it. Quadriderdad opened his, and they were solid plywood inside. Has anyone else opened theirs with either good or bad results. Also did you have any difficulties in getting them apart etc?? Wondering how much I do or don't need to do this. Insulating the floor made a huge difference in my ct's temps, will doing the doors make that much also? I guess that may depend on what is inside... 
