It’s hypothesized that as devices become more energy efficient, we’ll use them more because they’ll be cheaper to use. Called the rebound effect, it’s one reason why some people don’t think efficiency will do much of anything to curb carbon emissions.
Well, the American Council for Energy Efficiency thinks otherwise. They put out a white paper (summarized at the page linked above) that says the rebound effect exists, but that it’s not big enough to worry about. Ultimately, they say, we’ll still end up netting 80 percent of whatever efficiencies we gain. Sounds good to me, but I’ll reserve judgement until I see results that a) don’t come from a group with a vested interest in the matter and b) have passed peer-review muster.