Jevons' Paradox, also known as the rebound effect, suggests that as things become more efficient, we use more of them, say building a bigger house or driving a bigger car as the fuel economy improves. I never thought it would apply in a world where energy keeps getting more expensive; I thought we would logically be using the greater efficiency to basically stay in the same place.
I was wrong.
Every week I see yet another way people are using wonderful technologies like LEDs to waste energy in new ways. This truck is doubly egregious; it not only is burning gas to generate electricity to run a three-sided billboard selling condos in Toronto, it is adding traffic to the streets, causing everyone else to burn more fuel. I don't know whether it sells any condos but if I was stuck behind it instead of on my bike, I wouldn't think much of Greenpark Homes.
See a great summary of the discussion about Jevons' Paradox at RMI Outlet.