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.
Yeah I will be having external exhaust cards so that would be the best placement for them I was just using the 5970 model so I could get the sizes for the bar in the back to be in the correct place. For the fans to blow air down onto the cards and have the fan in the middle blow it out to the left and to the right is the best bet.