I was just reading on the Warhammer Online server architecture and hosting system in the Intel Zine. Fascinating description of what is essentially an AI simulation system with global deployment. Interesting are also the parallelization and maintenance systems. WAR uses application level parallelization and inter-process communication with TCP, forking of processes to deal with keep sieges and trying to minimize the instancing. The update system uses the hardware level access provided by blades, I am sure I would be scared if I was instructing the bios to eject and load a new CD and install a full os off it.
Luckily WAR is not so heavily populated and you can have some great large battles. The quality of the players is decent and the transition between RVE and RVR is smooth.
I wish similar efforts were put into dealing with real world problems and modelling it while we slept.