Mining compared to 2 years ago is more "efficient" given that the amount of transistors we fit on a die doubles almost every 18 months, decreasing power usage.

Think of it this way, Quad Core processors upon initial release were running on 125W to 150W (if I remember correctly), and now Intel and AMD are averaging 75W to 95W for twice the power. Now GPU's, given the way that they are developed (and are the primary tool of the current miner), can practically double their transistor count and cut their power usage in half within this time period.

My point in mentioning this (if it wasn't mentioned before, sorry I skimmed) is that even though miners are HEAVY users of power, the efficiency of all hardware is increasing while the performance is increasing as well. Seeing as it is clean, it's environmentally "friendly" if you're not considering every outside source of power production (.i.e. oil, coal, natural gas, etc.).

For many of you, like myself, have no need to turn on the heat during the winter because of all of the hot air my rig blows out!