Great to see this area getting some attention...
I have been thinking about these issues for some time now. My life involves sitting in front of a screen all day coding away. I myself have been trying to understand my personal impact on the environment, and on a larger scale, the typical developer's impact.
We have seen great strides on the hardware front (manufacturing, recycling, ect.), but I think the "green computing" world falls flat when it comes to the software. At least in regards to end-user desktop apps.
In response to Giles Jones:
"The 3D functions and eye candy of Vista result in more power usage."
This is a real issue. There is the suggestion to use efficient OSs like Puppy Linux, but I don't think this is the real solution. People use Windows and OS X. Some of us use Linux (and even efficient window managers), but most of the world uses very inefficient OSs.
"More efficient, 'greener' coding strategies could, ironically, also come from developments in high performance computing."
I think this is where the real savings will occur. We need better compilers, easer programming languages, and faster interpreters. We also need better learning environments for new developers so that they can take advantage of the "more efficient coding strategies". There are probably many areas that can be improved on, and I am by no means an expert here.
I think that solving these issues will require the input from a wide variety of disciplines (environmental engineers, software developers, corporate management, lawyers, etc).
I have been sitting on the http://greensoftware.org domain for a while now. This article has inspired me to put some effort into it. If you have any suggestions, or would like to help define the "green software initiative", then please stop by.