We had a session in MK on our recent trip (July 4th week.) We ended up with a not so great time slot (3:30) because I waited too long to book. As usual on summer afternoons, it was raining during our session, but our photographer had locations that worked in the rain, so we still got some great shots.
We asked for the castle area, and we took pics in 4-5 different locations. We asked for shots of all 4 of us and then some of our DD to mark her graduation. Our photographer took time at the beginning of the session to talk to us and find out our priorities and was super to work with. We were very happy with our photos, and I know had it not been raining they would have been even better.
A few tips--we wore coordinating colors and stepped it up a bit from our normal park attire. Girls wore comfy sundresses, and guys wore polo shirts and shorts. We didn't want to be too dressed up, which might look odd in a theme park photo, but definitely were happier with our pics than we would have been if we were in our usual t shirts and athletic shorts.
You can bring simple props-DD brought her mortar board and held it in some of her pics. They offered a chalkboard with her graduation year on it as well.
Overall, we were very happy with our session--even our 15 year old DS(who I typically have to bribe to participate in photos!!!) liked them and is already planning to have his graduation shots done in Epcot in a few years