My equipment can get fried by running it 24/7.
Correct me if I'm wrong, but I thought it was less stressful to keep a computer running constantly instead of turning it on and off. Something like the constant, steady voltage is less stressful than constant fluctuations.
That may or may not be the case with a typical CPU (i've heard reasonable arguments from either side) but when you're running 3 6990s at a time, they generate a lot of heat, with a lot of moving parts and there are a lot more things that can go wrong. Typical desktop computers are reasonably low-stress environments. When I've got this thing cranking, it sounds a bit like a jet engine. My guess is that it won't work flawlessly, continuously (what does?)... I'd love to be proven wrong, though.