NVIDIA's new GeForce GTX 580 feels to deliver what I would have expected from the original GTX 480. The card is blazing fast, especially in newer DX11 titles it often beats AMD's dual-GPU flagship Radeon HD 5970. This performance upgrade helps NVIDIA solidify its leading position in single GPU performance. Another major area that NVIDIA has worked on is power consumption which is over 20% advanced compared to the GTX 480, but there is still about 30% to go to lock horns with AMD's latest HD 6800 Series. NVIDIA has also improved the fan noise of their card, making it the quietest card in 3D load when compared to other high-end cards in this performance segment. However, this does not mean that the card is whisper-quiet or anywhere near it, the card is still well audible but it doesn't sound anymore like "warp core breach imminent" when heavily loaded.
A feature that will certainly be discussed at length in forums is the new power draw limiting system. When the card senses it is overloaded by either Furmark or OCCT, the card will reduce clocks to keep power consumption within the board power limit of 300 W. Such a system seems justified to avoid damage to motherboard and VGA card and allows NVIDIA to design their product robustness with real loads in mind. NVIDIA stresses that this system is designed not to limit overclocking or voltage tuning and that they will continue making improvements to it. Right now I also see reviewers affected because many rely on Furmark for testing temperatures, noise, power and other things which will make the review production process a bit more complex too. For the every day gamer the power draw limiter will not have any effect on performance.
In terms of pricing, NVIDIA is going with a $499 price point which is quite steep and essentially $450 for GTX 480 upscaled to GTX 580 performance levels. At this time the biggest unknown variable for potential customers is what AMD releases in the near future. If their high-end cards can not beat the GTX 580 in pricing and performance then NVIDIA has turned around the DirectX 11 boat and regained most lost ground against AMD.

Our review of two GeForce GTX 580 cards in multi-GPU SLI configuration can be found here.