I believe it's new for the free dining period. Only breakfast and dinner at Chef Mickey's any other time. I read on another thread that Disney is adding meals here and there to alleviate the crowding due to free dining.
My parents, brother, and 2 of his friends have a lunch ADR for 1pm on 8/13... I just booked it a few minutes ago (and am I going? NO!!! I'm being a good teacher and staying in my classroom for the first week of school ) It's fun doing all the planning though, trying to add "magic" here and there!
Hope you have fun @ the buffet- you'll be gone when I get a report on it though! If you see 3 teenage boys (2 6' tall, 1 5'4 or so) running around and getting character's autographs, that would MOST LIKELY be them!