Well, my GTX 460 and 400w corsair power supply arrived yesterday evening (225$ total before 30$ corsair rebate, I saved a few newegg coupons for the order

). Before I start talking about temperature I must tell you what kind of an enclosure it resides in now. It is a small dell case, not sure what atx compliant form factor it is, but a lot smaller than midtower. This case has one exhaust fan (two if you count the psu) and no intake. Also not my job of cable management with the long thick and numerous corsair cables was not the best.
Now that that is out of the way let me tell you a little about the temperature of this thing. When it idles, it powers down to 405mhz core, 900mhz shader and I cant recall the memory clock. This creates superb idling temperature, they stay within the range of 30-40C (I will update image when it is done cooling off, It just got done folding). Under load things are even more Impressive.

Be sure to enlarge imaged so you can see the numbers
As you can see, it will never reach or get over 70C. These tests are at auto-fan settings and were both at 40% fan speed. I can turn the fan up to 60% without hearing it, but why bother? this card runs cool on its own. bear in mind that this is at the core clock of 900mhz, and shader clock of 1800mhz. This is a 33% overclock on stock voltage, and i could go higher if I had the patience too, but again, i see no reason to. I can only imagine how high it could get with a simple voltage increase.
Performance wise I am seeing >30fps in most of my modern games completely maxed including 4x aa, such as battle forge, I have been able to go up to 16x AA (too lazy to force 32aa in drivers) in all the older games suck as bioshock and COD4. The only two games that i cannot get maxed are crysis and metro 2033, but they run fine on high settings (and 2xaa). I have yet to test spring yet, unfortunately. Folding at home is seeing 11-12k PPD coming from this gpu, so its certainly a superb folding purchase (low cost, low heat, low power and high PPD).
Did i mention that it is COMPLETELY silent below 65% fan which it never even need to approach? or that it cost me 195$ TOTAL for a psu and gpu upgrade.....or that or that or that......
The list goes on, this is a superb gpu in EVERY way. It gets my recommendation easily. A low cost, and low heat/power gpu that performs better than the closest ati competitor (5830hd) and still gets perks like physX, CUDA, good gpgpu performance and the option to go 3d.
edit: added idle temperature image.