Not bad .. but if you use all reference cards, they intake on that one fan. Since I only have anoying cards that exhaust out the front and back, I havn't been able to test a setup with those cards. I would think you'd get heat moving better just moving air front to back, ie bunch of fans blowing in the 'front' of the case (where the power connectors are on the cards) out the back. Would also help if you stacked these on top of each other, no need to draw air in from the top of each one. You could even put a shroud over the entire front and feed an air conditioner into it or something to that effect..
Could also save a little space by stacking the PSUs verticaly also.