The idea of seeing random strange families projected onto the castle just does not appeal to me at all. It would be great for the family in the picture, but who else? If I'm taking pictures of the castle I don't really want Joe Blow from Small Town, USA grinning back at me from one of the walls.
You know what would be cool?
To link photopass with your resort room, so digital pictures of your family enjoying their day would be up on your wall when you got back. If there were no pictures taken, the frames could be blank or have a generic scene.
This would be a great way to personalize and make it "your" room during your stay.