I was thinking along the lines of human energy consumption, e.g. the frustration I feel as I wait for pages to load and/or images to appear. If one could tap into an end users frustration of time wasted in this 'instant on ' culture that we have we could probably harness enough power to power major cities 10X over.

As far as actual energy consumption from electronic devices, while measurable I am sure it is minimal. More energy is wasted from devices that sit in a ready or standby mode for fast access; such as most modern televisions, stereos and other home applainces. However, there have already been steps taken to improve energy efficency through the purchase of Energy Star compliant products www.energystar.gov

To clarify: I was referring to the comment below

This might be the most irrelevant thing I've heard this week. If one were to compare the amount of energy a webserver uses with the amount of energy a printing press or a television broadcasting satellite uses, they wouldn't even be measured in the same denomination of watt/hours (kwH vs mwH. Seriously - someone is complaining that our computers are using too much energy now?

Bill Thompson’s article “The Offline Cost of an Online Life” describes how the technology we use is affecting the amount of energy we consume. On Wikipedia, for instance, the home page has 13 images that load when the page is viewed, an “inefficiency (that) costs 5000 kwh (kilowatt hours) per year, or around 2000kg of CO2.”
http://news.bbc.co.uk/2/hi/technology/7300403.stm
The basic premise – once you know how much and in what manner you are consuming energy, you can go reduce energy consumption by managing your resources better or perhaps just turning things off. Thompson thinks we need “a super-smart meter that can calculate how much power is being used serving my web pages, hosting my Facebook profile, running my Second Life avatar and, of course, dispatching my messages to my Twitter friends.”

That is probably true, since design is one of the first things one notices when viewing a new site, thus it should be the first thing one fixes to keep people coming back. However, the more multimedia and white space on a page are obvious signals of energy drainers anytime. It also, of course, depends on what kind of device one uses to browse on the internet.