FUD Zilla heard NVIDIA will equip the GeForce GTX 580 with a more efficient cooling solution than the previous one. Additionally, the site also heard that the launch is slated for November 9th and that it won't be a paperlaunch.
Many people don’t go along with Geforce GTX 580 name as the card should end up with Geforce GTX 490 or similar, but as you know Nvidia ups the numbers every year, sometimes even by simply renaming products. Geforce 200 became Geforce 300 without any significant change, but the Geforce 400 series have deserved its name.
Geforce 500 cards are a tweak, a real kicker so you will be able to tell the difference, especially with GTX 560 parts that should bring a lot of performance in sub $ (€)200 market.