With the next generation "Bulldozer" Opteron processors AMD will be adding features designed to lower the cost per watt of processing power, the most significant of which is the Thermal Design Power Cap, which takes the existing PowerCap Manager capability a step further by allowing power reduction without a corresponding performance reduction.
AMD also allows additional tweaking with an updated version of their TurboCore technology, which allows the processor to push harder at the TDP Cap and run at higher than standard performance levels. A complete explanation of how this technology works can be found on AMD's website.
It would seem that the goal here is for datacenter customers to be able to match processor energy usage to tasks, and to have the flexibility to change that matchup as necessary. A quite laudable goal, but one for which there is quite a bit of competition. It's not just worrying about the energy performance metrics from Intel that a datacenter CPU manufacturer has to worry about anymore.
As the drive towards greener datacenter gains momentum, vendors of other chip technologies have started to make a major push into the "match power to workload" space with a number of different technology approaches, ranging from multiple different implementations of ARM CPU technologies, to the dedicated appliance approach, where the CPU isn't the issue, just the overall power/performance of the dedicated device.
A lot of the issue won't be clearly defined until the forthcoming 16-core "Interlagos" and eight-core "Valencia" Opteron chips can be directly compared to the Intel Sandy Bridge technology CPUs already on the market. For the datacenter focusing on energy efficiencies, the actual workload per watt of consumed power metric might be significant in their purchase decision. Once that comparison is made, then other issues, such as managing the power capabilities of the Opteron CPU and ease of use of the flexibility and control will then become important, as well. But the window of opportunity for AMD in the datacenter may be rapidly closing as the pressure mounts from all sides.