I was in the new o2 arena on Friday night and noted they use a very handy method to serve the beer. It was similar to the way some of us bottle our beer from a bottling bucket with the long rod that goes into the bottle and then allows the beer to flow when a valve is pressed against the bottom of the bottle.
This method was similar. it consisted of a thick rod with a metal ball bearing at the bottom. The rod was placed inside the glass and the bearing pressed against the base of the glass, and hey presto a full pint in around 3 seconds. It was quite impressive really with minimal foaming and waste. It suited the Carlsberg perfectly, but Guinness was served the same way.... I heard few complaints.