Recently, Hadi Esmaeilzadeh, Emily Blem, Renée St. Amant, Karthikeyan Sankaralingam, and Doug Burger, published a paper entitled "Dark Silicon and the End of Multicore Scaling". Here is the associated article in New York Times that beautifully summarizes the issue:
"The problem is not that they cannot squeeze more transistors onto the chips — they surely can — but instead, like a city that cannot provide electricity for its entire streetlight system, that all those transistors could require too much power to run economically. They could overheat, too."