I just got back on Wednesday. DS is almost 15 months and nursed throughout the world. Examples: Haunted Mansion, Pooh, Peter Pan, Spaceship Earth, Carousel of Progress, TTA, Maelstrom, Indiana Jones, etc. I wore a tank top underneath my shirt (to cover the belly while nursing) and would just lift the outside shirt and pull down the tank top.
I did utilize the baby center at MK, HS, and Epcot. I love the one at MK. There was only one time that another mother was in there nursing (where as last year the room was always full). I was not happy one day when I went in and there was an entire extended family eating there lunch in the TV room at MK. There was not room in there for a family that would need access to the high chairs, etc. I also was not happy one of the times at HS. The nursing "room" is just a space blocked off by a curtain. There were 2 men and a child waiting for the mom to finish nursing watching TV. However, they were talking extremely loud and it was too distracting for my little guy and he wouldn't stay latched on because he kept hearing them. I also nursed DS in the bathroom at Camp Minnie/Mickey at AK. We were too far from the baby center and he was hungry. It was really hot outside and the bathroom was much cooler and had a bench inside it.
I did not use the Ergo like I thought I would. It was too hot to carry him around.
One suggestion--buy clip on fans from CVS (they are WONDERFUL). I clipped 2 of these to the top of DS's stroller and he NEVER got hot (while the rest of us were drenched in sweat).