I agree with molecular, but that's not the whole picture; I have a two month billing cycle, so I mine now and pay up to 60 days from now. Lots of time to convert to cash at the best rates (when the market isn't plummeting) and even do a little speculation of my own. No new 'out of pocket' money unless I'm mining at really large loss, bitcoins pay for it all, all the time.

Of course if I'm mining at a loss then the 60 day buffer with get me and I'll end up with 60 days of used electricity I don't have the bitcoins to pay, because I used the ones produced in the last cycle to pay the previous one...