Really, you're not seeing anything too different here to what you've seen in the past. The card looks very much like the last few high end NVIDIA cards; the GTX 470 and GTX 480 when it comes to the overall look. The cooler has been worked on, though, and we don't have that massive grill on the front.
To be completely honest, I loved the grill. It kind of gave that feeling of power. I'd just love to see a company use it if it was even just for cosmetic reasons.
The big thing about the GTX 580 is the fact that it's got 512 Shaders, which is what we all thought the GTX 480 would carry when it launched earlier this year. Word was that we ended up with 480 Shaders because NVIDIA struggled to get the chips to do 512. Whatever reason it was, though, we've got a card with 512 now.
Clocks have been bumped a little. The GTX 480 had a 701 / 1401 / 3696MHz QDR Core / Shader / Memory setup; the GTX 580 carries with it a 772 / 1544 / 4008MHz QDR setup.
Memory remains the same in both size and bus width which is 1536MB on a 383-bit bus. What you essentially end up with is an overclocked GTX 480 with more Shaders. There's nothing really new here.