We have been to the World about a dozen times (I'm starting to lose track!!) We had never gotten sick until our trip a year ago. We narrowed the problem down to when we ate at the Garden Grill (old menu). Hubby and I both had flank steak. Kids refused to eat it. I had a little and hubby had A LOT. Well, guess who was the sickest one? Hubby was sick all night long and could not eat anything the next day. He was pretty pale. I had a bit of nausea, but never actually got sick. I was so thankful that the kids refused to eat that steak, even though we tried to give it to them several times. The steak tasted good, but must have had something wrong with it.
We weren't really upset at Disney since I guess it can happen when you eat out at any restaurant or buffet. It's surprising it doesn't happen more often when you consider the amount of food that flows through WDW.