VMware's worked it out and says that its customers have virtualized more than nine million workloads since 1998. That means an estimated energy savings of 105 billion kilowatt hours of electricity, or roughly $11.6 billion.

And according to the CIA World Factbook, that's equivalent to all the power consumed in the US in 10 days.

The company is developing a penchant for this kind of comparison. Last week, in unveiling its next-generation vSphere widgetry it said that if its installed base went over to vSphere the power saved would equal the power Denmark consumes in 10 days.

Anyway, it claims its virtual infrastructure helps enterprises and governments cut their energy costs and consumption by as much as 80%. And says most desktops and servers today are in use only 8%-15% of the time they're turned on, but consume 60%-90% of the normal workload power even when idle.

This point brings VMware around to vSphere's advanced resource and memory management which is supposed to enable consolidation ratios of 15:1 or more and dynamically power off unneeded servers, which in turn increases hardware utilization to as much as 85%. And of course VMware points out that every server retired from a datacenter saves four tons of CO2 emissions, which is the equivalent of taking 1.5 cars off the road or planting 55 trees.

Similar savings are available for desktop PCs, which can be consolidated on servers in the datacenter using VMware View.

VMware says it works with more than 40 utility programs worldwide to offer financial incentives for virtualization projects in data centers. The incentives are based on the amount of energy savings achieved through data center consolidation and qualifying customers can earn a maximum rebate amount of $4 million per project site, and $300-$600 in annual energy costs for each server removed. It says those savings are almost double when reduced data center cooling costs are also taken into account.

It's got a lot of examples.