Google published its 12 month trailing power usage effectiveness (PUE) figure for 2011 today. It clocked in at 1.14 a hair improvement over its 2010 PUE of 1.16. I think we may be hitting diminishing returns with the old PUE measurement, particularly at energy conscious webscale companies like Google. It’s time to start looking at the efficiency of the servers themselves, and thinking about performance per watt. Basically, how many computations are you getting per unit of energy, and could code be better written to be more efficient? But I applaud all Google has done to hold itself and ultimately, other companies, accountable for its data center energy efficiency.