You can make ADR's for the Plaza...I have some for our upcoming trip...
IMHO, The Plaza is a great place to eat!
When making my ADR's the guy making the ressie laughed and said that the Plaza was one of the best secrets of MK...Apparently, not many people give it a try...
It is a reasonably-priced (for Disney parks), great meal. I liked their milkshakes better than Beaches and Cream or the 50's Primetime...
It should not be hard to get an ADR there. My Dad and I went there for lunch in August 2006 which happen to be during free dinning that year and we were able to make our ADR there while in WDW, at the last minute.