The PCI-SIG has finalized the specifications. We should likely expect to see chipsets by Q3 (Intel's "Bearlake").

"Doubling the interconnect bit rate increases the aggregate bandwidth of a single PCI Express x16 slot to 16 GB/s. PCI Express 2.0 is also backwards compatible with older versions of the standard, meaning that consumers will still be able to use their older hardware in slots based on the revised standard."