James Hamilton from Microsoft has put together an interesting analysis of power costs as a component of overall data center expenses. James makes the point that electric power is often described as the number one cost in a modern mega-data center, but actually trails servers and the power and cooling infrastructure in the overall percentage of monthly data center costs.
But he also provides a broader context for the hard numbers, defining the "fully burdened cost of power" as the sum of the cost of the power consumed and the cost of both the cooling and power distribution infrastructure: "Since power and infrastructure costs continue to rise while the cost of servers measured in work done per $ continues to fall, it actually is correct to say that the fully burdened cost of power does, or soon will, dominate all other data center costs," James writes.
James has shared the Excel spreadsheet he used for his calculations, so you can plug in your own numbers. His analysis is also being discussed at O'Reilly Radar.