Saw this and was interested. I know at least my card in the past when I had 2 monitors hooked up it idled at a higher voltage/clock speed (mines an AMD card though). Curious if nVidia did the same? The GPU clock wouldn't nessisarly increase but I'd always notice the Memory going to full gaming clock speeds and voltage would bump up a few ticks.
Otherwise I personally didn't see any other effects of having 2 monitors or more hooked up. I run 3 montiors at work (2 discrete GPU + 1 Laptop with onboard GPU) works out very well but its a professional card in it.