Saving on power in the datacenter is one of the worst ways to try to save money, in my experience.

It varies greatly, but $10 million dollars worth of servers, network gear, and storage might cost $25k/mo in power. Shaving 5% or 10% off that bill is practically meaningless. You can save a lot more money in other ways.

Obviously at massive scale (think Google) it's a different story, but for the average small-medium company it's not even worth thinking about until you've gone after everything else.