I have made this walk in the June heat last year. I am in pretty good walking shape and didn't feel any stress at all as I walked from MGM to Epcot. My wife thought I was crazy. Of course, I did stop in and have a beer at the ESPN Club. The walk is faster than the boat, but if you are tired from walking at the parks, the boat can be a great break. If you are in a BIG hurry, walk. If you want to relax and enjoy, take the boat. I used to have the Disney theme park commando attitude, but I realized this: they are not going to move WDW, and I can (and will) go back.