Notice blockchain.info uses an average power consumption of 650W/Gh/s to calculate the "profit margin". That power consumption estimate is 60 to 100 times too high.
The sad part is blockchain.info has been notified about this error numerous times by numerous people, including the venerable organofcorti, but blockchain.info apparently doesn't care. Occasionally the MSM picks up this inaccurate number from blockchain.info and provides fuel for the naysayers and doubt for the curious.
All of which isn't to say you should get another miner. DeathAndTaxes has a thread somewhere showing the difficulty point where each of several named mining rigs should be turned off in the future because their BTC return will be less than the cost of their electricity consumption.
But that's not true for the network as a whole, yet, not by a long shot.