Two interesting blog posts:
Chirag Mehta: Greening the Data Centers
Microsoft: Charging Customers for Power Usage in Microsoft Data Centers

Also, Google has publicly released its data center efficiency measurements, as part of their docs on their commitment to sustainable computing. What they don’t say is the degree to which their green efforts impacts the availability of their facilities. Google can afford to have lower individual facility reliability, because their smart distributed infrastructure can seamlessly adapt to failure. Most enterprises don’t have that luxury.