Google is declaring war on the power supply. Power supplies are notorious for being watt suckers, with efficiencies of 20 percent on the low end. This has been discussed before, and there's even a group called 80plus that is dedicated to getting power supplies up to 80 percent efficiency. We will see how it works out.
Of course, one of the biggest power wasters is the conversion from AC to DC current, and vice versy. For example, incoming AC power is converted to DC by your uninterruptible power supply (UPS). Then it gets converted to AC going out of the UPS. Then it gets converted again by your computer's power supply to DC for the motherboard. A recent study suggested that you could save up to 20 percent if you run a DC-powered data center, skipping over the individual power supplies for the computers.
Power is one of those things that people think is just there, and it's cheap to boot. What will get companies to change their minds? Well, if it's not cost savings, it might be the government, who is starting to take a look at data centers and the power they use. It's all fun and games until the regulations get published.