The chef will take you around at the buffets and show you what you can and can't eat. They're ok about it. I never got any GF buns or rolls or waffles or anything, at any buffet, like people talk about getting. I don't eat that stuff at home most of the time either, so no big loss, but with all the walking at WDW I started to feel a little carb-starved. I felt awkward, I really hate discussing food issues with strangers, so I basically said nothing except asked them to please show me what items did not contain gluten.
H&V - The buffet breakfast at H&V was the worst. The potatoes were gross, the fruit was gross, the meats were gross...I think I ate scrambled eggs and yogurt. I left hungry. This has scared me away from any of the TS breakfast buffets.
1900PF - not super great for me GF. Not awful, and there were some yummy things, but nothing special. Lots of salad type stuff GF, so that's nice. The meats are like Golden Corral level to me, so, very meh. Not worth paying for, but ok when you have FD.
Boma - is awesome GF, as long as you like that kind of food (which I do). Worst part is that zebra domes are not GF and you have to look at everyone else eating zebra domes. Actually I had eaten one on a prior trip and didn't think they were that great, but they sure look delicious anyway.
Marrakesh - I'm solely basing my opinion on our QS Tangieriene Cafe experience, but I would NOT eat here or anywhere in "Morocco" if I had celiac - I do not trust their understanding of the issue. My husband even explained it to them in Arabic and they still did not really seem to understand. This was the only QS place in WDW that really didn't even seem to understand the issue, and just based on that it has kind of scared me away from Marrakesh, too.
Biergarten - pretty awful for GF if you do not like sausage. I do not like sausage. Our server was really nice and the singing was fun, but I left hungry.
Tusker House - was pretty good GF. I'd eat there again. Not nearly as good as Boma, but really good considering it's a character buffet.
Prior to our last trip, I was worried about how GF QS would work. It turned out to be really good, easy to order GF almost everywhere. The only problems were at Tangierine Cafe, where they were really nice but just didn't understand, and at POR QS (I can't remember what their main QS is called) - they just flat out were unhelpful and said they'd have to call the chef, wait for him to come out, which would take a while, and it would take 20 extra minutes for me to get anything GF. They made it out like it was an enormous undertaking.