This was my favorite thing about Cologne. The server would make a mark with a pencil on the paper tablecloth everytime they dropped a glass off, and you got a continuous supply of cold beer. You paid at the end based on the number of hashmarks. The trays are also really neat - they have holes that are the perfect size for the little glasses, so nothing spills.
Also: Humphry Slocombe got a kickass writeup in the NYT. Yay, Humphry!