I have a mFi power strip so I don't know how accurate it is compared to a kil-a-watt but it says that the miner is drawing 497/498 watts overclocked to 500Gh (650 mhz core clock).
For comparison it says the raspberry pi is drawing 2.5 watts
How are they going to use the power supplies that they showed at the factory all those months ago for the Sierras. Weren't they 750W power supplies? If the sierra will draw 1500W it is going to need two 1000W psus to power the boards.