One thing that struck me at last week's AdvancedTCA Summit in Paris was Intel's Keate Despain's focus on performance per watt during his keynote address. What a change from just a few years ago! And it's not just Keate Despain, or the AdvancedTCA audience. CPU performance per watt has finally become a significant competitive issue. A quick Google search on "performance per watt" returns more than 2 million results including two paid ads, one by Intel and one by AMD.
I love it. For years, I've pushed our engineers to focus on performance per watt and to this day I have a running argument with Texas Instruments over their C6x series DSPs (which are optimized for performance rather than performance per watt).
This has nothing to do with being "green." Every system and subsystem has to fit within some power budget. At one time, a plug-in board for an IBM PC was risky if it dissipated more than 15 watts. Until recently, carrier hotels (for example) had cooling for 50-150 watts per square foot. 3000 watts per rack was a big deal. Try putting an IBM blade server in that! You'd be hard pressed to support ten CPUs in an entire rack. [Interesting discussion here (free but registration required).]
In my experience, if system architects focus on performance per watt, you end up with designs that are also competitive on density and cost, but it seldom works the other way around.