So, according to the blockchain.info estimate, the average power use is 40.7 MW, which is based on 650W / GH, or 1.54 MH / J.
That would be a reasonable figure, if the network were still primarily GPU-based. I think they should update that page to reflect the entry of ASIC hardware, which is almost certainly responsible for the two-fold increase in hash rate over the last couple of months.
I'm sticking with 15 MW as a better estimate.