http://www.pcisig.com/specifications/pciexpress/base2
Mainly a doubling of bandwidth, but a few others....
Quote:
* Dynamic link speed management allows developers to control the speed at which the link is operating
* Link bandwidth notification alerts platform software (operating system, device drivers, etc) of changes in link speed and width
* Capability structure expansion increases control registers to better manage devices, slots and the interconnect
* Access control services allows for optional controls to manage peer-to-peer transactions
* Completion timeout control allows developers to define a required disable mechanism for transaction timeouts
* Function-level reset provides an optional mechanism to reset functions within a multi-function device
* Power limit redefinition enables slot power limit values to accommodate devices that consume higher power