Was making $1.5mm, in October of last year. There are some off the cuff calculations in the reddit thread [0] that indicate the same setup would currently be netting only about a tenth of that amount now.
Based on the video, it looks like these guys likely swap out for the newest equipment as soon as it makes sense economically.
If I were making such an investment, I'd think carefully about the rate of computational depreciation (which is predictable) and probably hedge on the price of power. The only unpredictable thing in this setup is the price of bitcoin, which I believe they're extremely bullish on long term. You could probably figure out a way to hedge that, too, if you could find someone to take the action.
0 - http://www.reddit.com/r/Bitcoin/comments/2v02n9/life_inside_...