X-bit Labs reports AMD's Bulldozer Opteron processors will feature an adjustable TDP:
Advanced Micro Devices' next-generation Opteron microprocessors based on Bulldozer micro-architecture will support capability to adjust maximum thermal design power (TDP). The technology will allow customers to regulate TDPs in order to balance power consumption and performance of data centers.
Today's AMD Opteron processors allow turning off processor states in order to reduce power consumption, though that ultimately can lead to somewhat lower performance. Still, some large server users value power efficiency higher than pure performance. AMD promises that code-named Interlagos and Valencia will be able to reduce the TDP and maintain performance level of the chips.