We sailed on the 3/14/15 Summit with my celiac mom. We notified the ship in advance and let all the waiters know when she placed her orders. We had lunch the first day in Bistro on Five. They were able to bring her the crepe filling.
Overall, she was really pleased with the offerings. In the main dining room, each item has symbols next to it with the dietary information (gluten, dairy, vegetarian or sugar-added). The waiter was very knowledgeable. Each night, she would get a copy of the following night's menu to know whether she would need a special order. She never did since there was large variety.
We even had great success in Blu, Normandie and QSine although their menus don't have the special symbols. The chefs of both specialty restaurants came to our table to discuss the options. The Maitre'D at Qsine has children who are celiac so he kept a careful eye on table and answered all our questions. He even intervened when the person delivering the course wasn't quite sure what was gluten free.
The buffet was less successful. She eventually was able to find a manager to give her a tour of what to eat. They did offer to go back into the kitchen to prepare her toast or other items, but that would take about 20 minutes. The pizza was terrible. Probably a rice flour that was spongy and no flavor. The one day she wanted to get gluten-free pasta, they said they were out of it that day.
The Gluten free bread varied a lot in quality. She got some great bread in Normandie and Blu - but the main dining room was not as good.