The Rebound Effect is a significant problem in energy policy and sustainable design: if new devices are more energy efficient, will users simply use them more, or leave them on for longer? (A kind of Jevons' Paradox). This UK Energy Research Centre report (PDF, 5 Mb) looks to be a comprehensive, interesting and readable treatment of the subject.
The compact fluorescent light bulb shown above, fitted under some scaffolding over a public footpath in Hurley, on the Thames near Henley, is switched on all day, even in bright sunshine. But that's 'OK' of course, because it's one of those energy-saving bulbs.
How prevalent is this kind of thinking among users?