I don't know of any system that gets close to .5W/GH.    Butterfly Labs isn't trustworthy and is many months behind on shipping.   The S3 from Bitman seems to be the current best on power consumption (~.7W/GH).    Even then that is just the primary power, you also have to pay for cooling.    It doesn't leave room for other maintenance costs and staff.    Also I used an impossibly low cost for electricity.    More likely it is closer to double what I used, even in Iceland.  (If that is really where they are.)