Had my card a couple of days now. It's idling between 33 and 38 degrees, and it's never gone above 73 degrees with the fan at stock auto settings (it's stayed on 47% the entire time), even playing Metro 2033 on high in 3D.
I haven't done any testing such as Furmark, but I haven't seen any artefacts in the games I've tried - Metro 2033, Lead & Gold, Dragon Age Origins: Awakening and some free MMO called Black Prophecy.
For those interested, my case is a Fractal Design Define R3 with an added side 140mm fan and an added top 140mm fan. The PSU is a 650w Antec TruePower New. All my power phase LEDs are on even while doing nothing, but the temperatures are very low. The card is absolutely silent at anything below about 44% fan speed, and is only just audible at 47 - 48, so I imagine anything up to about 60% would be fine while playing games...
Edit: Just read about the buzzing. Mine does that as well, but only on Dragon Age for some weird reason. I never noticed it on any other game or with the 460 that this card replaced.