Isn't it just a matter of time before the cost of electricity becomes higher than the value of mined bitcoins?
In the short run, say next six months, the trend will be more professional data centers. These have economies of scale and cheap electricity. Obviously Average Joe will not make money anymore with his Antminer.
From 2015 I believe even the data centers will lose. People with free electricity will learn that mining generates a "free" income. Some have free electricity on their rental contracts. Others are illegally connected. There will even be some who deliberately mine at a loss. Say you own a business. The cost of electricity reduces the profit, hence taxes, while the mined bitcoins are never reported. For employees it becomes even more lucrative as the employer takes the cost.
These ways of mining are mostly illegal, but I believe enough people will do it anyway. Another, more honest, use of miners is for heat. Canadians, Scandinavians and Russians should all be mining