Power draw, temps, and noise
Adding a second card into a mid-range system increases frame-rates, clearly, but what does it to do energy consumption and temperatures?
The numbers don't paint NVIDIA's newest GeForce in a positive light. Crysis load is some 47W higher - at the mains, mind - than a couple of performance-comparable Radeon HD 5750s.
Putting a second card into the rig also means that temperatures rise a little, but they're nothing to worry about.
A word on noise
Two graphics cards are always going to be louder than a single card. Housed inside a Corsair Obsidian 700D chassis we ran Crysis Warhead and subjectively noted the noise. The Radeon cards were slightly noisier than the GeForce duo. However, we'd be more than happy gaming on both machines and would expect well-engineered system integrator-built PCs to be quiet.