I bought this card to replace my ageing, and very noisy, XFX HD4870. I've had the card for about a week now, and I can't praise it highly enough.
When I turn on my PC now, I have to actually check that he power light is on, as the noise has dropped to imperceptible levels since installing this card. Not only is it quiet when idling, I've also pushed it as hard as I could using FurMark, and I'm pleased to report that the fan noise increased just enough to make it audible, but not nearly so much that it would ever distract from anything but the quietest moment.
You'd think that a quiet card must be running hot; everyone knows you don't get something for nothing... Well with this card, it seems you do! In the FurMark test, I saw the core temperature climb as expected, but it levelled off at around 65 degrees, which is nowhere near anything I'd worry about. When you consider that FurMark is designed to push GPUs to their absolute limits, then you'll understand how impressive this performance is.
I haven't played any really graphics intensive games on it yet, but my performance in Civ 5 has improved immeasurably, and that's with my options turned up from medium to max!
All in all, I can't say anything other than this is one of the most impressive PC components I've ever bought in 10+ years of building my own systems. Anyone who buys this card has bought a winner!