Green Data Centers: Good for Pocketbook, Good for Planet, or Both?

Green IT has taken off, with many products and services dedicated to saving energy in data centers.

Some green initiatives are strictly ideological, with an eye towards doing what is best for the environment without addressing the financial cost.

In Europe, a group of global IT firms are pooling their knowledge to create a green guide to all aspects of the data center (full article here). No mention is made in the article about where these environmentally-friendly practices fall on the spectrum in terms of price tag (more than standard, less than standard, same as standard).
Some green strategies only focus on how to save money, without a particular emphasis on the environment, although the two are obviously linked. The story How to Green Your Data Center without a Forklift, by Wayne Rash, makes the following case:

“Fortunately, there’s a lot you can do to cut your energy consumption for maximum impact and with minimal attention and effort. Even better, some of the most effective areas of energy savings don’t involve expensive new servers and upgraded cooling.”

The green IT company Viridity approached the issue from both perspectives, making the case that green IT is better for wallets and the environments. According to this article on eWeek:

“Viridity officials say their software will be able to reduce operational costs of data centers by as much as 40 percent and extend the life of data centers by several years.
Major tech players—including IBM, Hewlett-Packard and Dell—are rolling out their own green data center services, aiming to help businesses reduce energy consumption and cut costs.”
This argument is obviously the most compelling, as it speaks to the moral ground as well as bottom line savings.

Is it true? In your experience, does going green for your IT needs make sense financially, or does it necessarily come with a higher price tag?