How many GH per watt do ASICMiner et al get?
It's quite variable, based upon the stats in the main chart ("Complete ASIC Hardware")
http://mining.thegenesisblock.com/ASICminer (blade) is 7 Watts/GH, Avalon 10, BFL 6, BitFury & KnC 1-1.5
So, the mining power consumption has broadly been in 3 levels:
650 W/GH until end-Feb
8 W/GH March through June
2 W/GH Since July but will drop below 1 early next year.
Rough numbers, but perhaps usable