Hey guys, just came across this thread recently so I figured I'd chime in.
I am the person that put this rig together. It was designed from the ground up to be an HPC solution, rather than a gaming platform, so with the latest NVIDIA GPUs, we can use it for general purpose computing applications. Without SLI, we can actually utilize all the memory on all of the GPUs for use in applications.
The picture you guys see there is our prototype system where we used 6 GeForce 8800 GTS cards with 640MB each. Yes, there is only 1 power supply. The other boxes in the front are CoolIT's radiator boxes. We have 3 of them in there. One for the top 3 GPUs, one for the 2 Xeon quad core CPUs, and one for the bottom 3 GPUs.
I just got my 6 Tesla GPUs recently so I'm just in the process of setting those up and testing them out.