Reducing or controlling the high cost of the power to run and cool computer hardware is a top priority for many organizations throughout the world. Many organizations are considering server virtualization solutions to reduce their server footprint and the associated power and cooling costs. Because the virtualization of Microsoft Exchange servers rarely results in a reduction of physical processors, there is some question whether there is significant hardware, power, cooling, or space savings from virtualizing correctly sized Exchange Server 2007 server roles.

More info: TechNet