I bet the cooling fans on those 1U servers sound like a jet engine. They're loud enough when you're cooling a 125W CPU, let alone 2-4 250W+ graphics cards.

I myself like 3U or 4U chassis in most cases. They let me use more of the card slots than a 2U chassis (ks 2915, raid, ethernet, 24 bit I/O card, and a rs232 card), and you can generally get them with a standard ATX power supply as well.

Given the configuration and lack of space in today's real world racks it doesn't look promising.

With some vendors, like IBM, you could not put many of those 1U in a rack since the cabling interferes with hot air exiting in the rear.

2U or 4U with lots of internal space and big heat spreaders yes, but 1U coupled with almost 100% utilisation looks bad. And if you don't have full util with that sort of hardware, don't even buy it.