We went in July, on a 2-week total trip but only 5 nights were at Disney. We had driven down from NYC, and went to southern Florida to visit family first. However most of my "bad" eating was at WDW. I was very good, for the most part, on the rest of the vacation so that I could allow myself to indulge more at WDW. I gained a total of 4 and a half pounds on the trip. I clicked on 3-4 though since even though I was pretty good the rest of the trip I am sure at least a little of the gain was also from the other days of our vacation. I attribute about 3 pounds to the 5 nights we spent at the world.
Oh I will also add that regularly at home I follow Weight Watchers maintenance, and work out 5 days per week pretty hard. So on vacation my habits are drastically different than at home!
I anticipate 5 or more pounds on our 10-night trip in July 2010! I love the food at Disney!!