David Roberts provides an excellent overview of recent studies touting both the incredible impact efficiency can have on greenhouse gas emisisons:
"Energy efficiency investments can provide up to one-half of the needed greenhouse-gas emissions reductions most scientists say are needed between now and the year 2050."
and its inherent profitability for the economy:
"Hence, shifting away from the production and consumption of conventional energy resources, in favor of more productive investments in energy-efficient technologies, can lead to a more robust economy and to a greater level of overall employment opportunities with the U.S."
Roberts also highlights this choice quote from Joseph Romm summarizing the results of the McKinsey study on energy efficiency:
"the entire 2020 target in the Waxman-Markey climate bill could be met with energy efficiency at a net savings to U.S. consumers and businesses of $700 billion."