Broadly speaking, there are two main reasons for companies to go green. The first is to reduce energy costs, thereby saving the company money. As one IT executive put it to me recently, "Green computing is all about saving greenbacks."

In this view, computing equipment essentially converts kilowatts to CPU cycles, so the trick is to increase efficiency so that more CPU cycles are created from the same number of kilowatts. This can happen in a number of different ways: by deploying virtualization to increase utilization (a powered-on server that's not utilized consumes about half the power of a fully utilized server); architecting data centers to minimize AC requirements; and consolidating systems and facilities.

The second reason for a company to go green is to reduce its overall carbon footprint, which may or may not also reduce overall costs. For example, Cisco recently announced the goal of reducing the company's carbon footprint by 25% (as benchmarked against its 2007 levels) by 2012.

One really great way for an organization to reduce its carbon footprint is to increase its use of virtual-workplace technologies: videoconferencing, Web conferencing, unified communications and collaboration, presence, and mobility. These technologies reduce or eliminate the need for physical proximity, so employees don't need to travel (and in particular, commute) as much. (Is it a coincidence that Cisco makes telepresence gear? You tell me. . . .)

It's often possible to reduce reimbursed travel and facilities costs by using virtual-workplace technologies. If, for instance, a company holds a telepresence meeting instead of a paid business trip (as the folks at Cisco increasingly do) the result is direct travel savings. And if virtual-workplace technology enables a company to house employees in less-expensive suburban locations rather than expensive downtown offices, the facilities savings can be considerable (it costs upwards of $20,000 per employee, per year to provide office space in major metropolitan areas — more than many companies' total per-employee IT budget).

More likely, however, is that virtual technologies simply cut down on commuting costs, which are typically borne by the employee, not the company. The strongest business cases around virtual-workplace technologies don't stress travel reduction. Instead, they emphasize productivity and agility: Employees are able to make more informed decisions, or make them faster.