Regarding the Buffet Diamantino. I just happened to have one of their fliers. There were guys all around the Prado and Atocha passing out these yellow advertisements. I took one and put it in my guide book. Here is what the flier say:

1100 Pesetas for all you can eat. 20 different dishes. Meats, fish, salad, chicken, pasta, paella and desserts. Open 1-5 and 8:30-11:30. It is in the plaza right by the Anton Martin metro stop.

We didn't eat there, somehow the idea of an all you can eat buffet just didn't seem like it would be part of the Madrid experience. We did eat in lots of great restaurants, and after a week, I think I sampled everything I wanted, but in a more leisurely, less gluttonous fashion. But now that I am back in the States it's back to the Pizza Hut buffet!

Ed