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 percent (as benchmarked against its 2007 levels) by 2012.

One really great way to reduce your organization's carbon footprint is to increase your 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 to US$20,000 per employee per year to provide office space in major metropolitan areas -- more than many companies' total per-employee IT budget).

But more likely, 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.

All that said, though, cutting down on commuting by mandating effective telecommuting is one of the best ways to reduce your carbon footprint. The average American takes roughly 50 minutes to commute 32 miles (both figures roundtrip). Converting just a fraction of those commutes to telecommutes can dramatically reduce carbon consumption.

But it's easier said than done: Only around a quarter (23 percent) of the companies I work with say that corporate green policies are encouraging people to telecommute. Yet the evidence is strong that these corporate policies are effective. Companies that mandate telecommuting have roughly 36 percent more telecommuters than those that don't. And they're considerably more likely to make use of virtual workplace technologies than those that don't.

Bottom line: If you're going green, plan to go virtual. And make it a mandate.