The official spec for PCI Express 2.0 has now been released, bringing with it significant boosts to the interface. The total capacity of the PCI Express 2.0 bus will be 5Gbps, twice the old standard, and an x16 connector will now be able to achieve transfers as high as 16Gbps. It will be backwards compatible with PCIe 1.1 cards, making it simple for motherboard manufacturers to transition to it in the future. Intel is already expected to offer 2.0 chipsets this year.
Various other improvements were also made, including dynamic link speed alteration and more "interactive" features of the bus in communicating with software. Cool stuff.