Well, my group has been trying to get a group of 20 together for a lunch. The only place that we could find that would work with us and was reasonably priced was Rainforest Cafe or T-Rex. We know the food is sub-par, but the food is secondary to us all getting together...plus the kids will enjoy the atmosphere. We had to go through group sales. If your group is over 20 people then they have set 3-course meals that includes entree, drink and dessert for a set price. I think there are about 16 different items to choose from at 3-4 price points. We are having our get together at the Rainforest Cafe at AK because several of us will already be there at the park, but others are coming in from Orlando just for the lunch. PM me if you want more details!
As a side note....we are considered a Grand Gathering and could not get any real help from them. There are the dessert parties, ect...but those were all out of our price range. We also contacted convention services....and the price was VERY high to organize something for our group. Most places at Disney cannot accomodate a large group because the restaurants are on the small side.