The company I work hosts a decent size data center to support its business (a website hitting around 1.5Mil hits a day, and countless business applications to keep the company in business). Around the end of last year our backup-power (UPS') and air-conditioning were hitting the alarming 90% level (this is understated!).
The issue wasn't the number of production servers, but rather the pre-production servers for Development, Testing and Staging. Replicating the rather large interconnected complex environment took hundreds of servers, all at 5% CPU utilization most times during the month!
Our Savior: Server virtualization
Just by converting as many pre-production servers to virtual instances and hosting these on decent machines, we saw a reduction to below 45% capacity. The additional benefit is that many of these machines were hosted on poor, unstable hardware previously - virtualized, these are running on solid hardware and in many cases perform better than they did.
If every company house that has software development and testing server resources virtualized their pre-production environments imagine how much less power our server rooms would consume. That has got to be better for the financial operating cost and also better for the environment in general!
Troy.