I don't remember when they added it (I think it was when they added princesses to lunch or dinner), but I know they had it in Dec06.
It's not a full buffet of the food - the hot food (eggs, potatoes, sausage, etc) is still brought to your table by the server. The buffet is for "cold" items, like pastries, lox, etc. Kind of the appetizer/salad before the main course.