The key thing about PCIe 2.0 is that you can get a bit more power from the PCIe slot. The current PCIe 1 and 1.1 specification will limit you to 75W and it is quite obvious that you will need even more in the future.
Cards such as Geforce 8800 GTX and Radeon HD 2900XT needs the whole 75W from the PCIe port and have two power plug that can bring total of 225W to the graphic card. With PCIe 2.0 specification you will be able to add even more power to your greedy graphic card and this is what the future brings and needs.
PCIe 2.0 chipsets will be launched September to October time and RD790 and Intel’s X38 are the first two to bring the PCIe 2.0 to AMD and Intel platform.