I did it in April and had lunch at the Brown Derby with Laura Alletag, a Project Manager, Sr. Laura is currently overseeing Mickey and Minnie's Runaway Train at HS. Before that, she was the Project Manager for the Toy Story Mania expansion. Learned a ton about how projects come about to being completed. She was able to talk about TSM but unable to give us details on the new ride opening in the Chinese Theater, bummer but understandable. It was fun and informative, with a tasty menu to boot! I recommend taking the time if you can get a reservation.
I've done it twice. I'd recommend it to anyone, but especially recommend it to solo travelers. Both times I was pleased with the experience, but the success of the event does depend on the Imagineer you get and the other guests. I think the one Imagineer did edge out the other because he we better at engaging everyone at the table into the conversation and the group of people in that session were extremely interesting and informative. The other time I went was really good too it was nearly an identical mix of people, but the Imagineer didn't engage everyone in the discussion as much as the other one did, but it still was excellent.
I also find this to be a pretty good value as the cost is pretty much on par with what you would pay for this meal otherwise. Plus you get the added benefit of a learning experience, good conversation and getting to eat your meal peacefully in the comfort of a private dining room.
I've done it once. I forgot who the Imagineer was (by name) but I have his autograph on the black plate (souvenir). It was great. There were the 3 of us and then a single person and then a family of 4 or 5. So 9-10 people + the Imagineer. Friend was very talkative, asked questions.