We just got back from a Grand Gathering. We signed up for 3 of the 4 events, and when we checked in, we recieved an itinerary with our scheduled items. One was missing, and it took a while before they could "find" it. Thankfully, the CM helping us was very patient.
As far as the Grand Gathering events are concerned, we really enjoyed the Magical Fireworks Voyage and the Safari Dinner. The pirates on the fireworks voyage were GREAT! Also, our kids were SO excited to meet Peter Pan. We also did the Good Morning Gathering, but found that to be less entertaining. Still good if you haven't met many characters yet. We originally had scheduled it for the first day at MK, but Disney called us and rescheduled it for our 5th day. So, our kids were not as excited to see Chip & Dale again. But, we still had a good time.
One suggestion about traveling with a large group. . . don't try to stay on the same schedule. We found out after day 1 that we couldn't do that. Each of our kids are different ages (ranging from 2-10) and the younger ones definitely needed bigger breaks during the day. The best part is that you are at the greatest place with all of your loved ones. . . have a ball!!
