One thing that really amazed me about PunBB was how fast it is. It is also one of the reasons why I chose it as a conceptual starting point for developing PhunkyBB.
I've wondering for some time how it achieved its speed, especially since it does use a lot of div and table tags, as well as a substantial amount of CSS.
A moment ago I was editing some CSS for PhunkyBB and it dawned on me that the speed may be due to how specific the CSS rules are. I'll have to do some research and testing to validate this assumtion.