They are lovely places. They are generally located neat the first aid areas, and have a secluded peaceful room to breastfeed in with rockers. There is an area for older kids (toddlers) to play it with a tv while mom may be bf, getting medical care, or whatever, and baby supplies that are priced a little higher than normal. But, if you forget your supplies, it's nice knowing that you can get supplies in the park.
MK's is nice, if a little dated and located at the First Aid center by Crystal Palace. Epcot's is by the old Odessys place by Mexico. It's bigger, but a little sterile looking. The BF rooms are bigger. DHS is the smallest and near guest relations/First aid in the front of the park. BF area is very small, if I remember correctly. The AK is the nicest one of all! It's near the front area, on the left hand side side of the park and before the old camp Mickey Minnie. It's very open, and has great BF area.
You have to leave strollers outside, and there are cm there to assist you. They are very nice, helpful, and supportive. They are perfect places to take breaks and are more than just a diaper change area - they are fully functional centers that are supportive of moms and baby needs. I love them!