Re: pie-in-the-sky idea to make a real salary with bitcoin mining
And I still wouldn't be out of the hole to buy new mining equipment to stay on top of the difficulty curve. Bleh.
Personally, I think you're thinking about buying the wrong equipment. 
Optimizing based on the best Mhash/s per W, the 5870, and discount retail prices on equipment, running at 200W before the GPU load, you will need 1975 5870s @ $190 ea. and 395 base systems @ ~$421.97. Your CapEx will be $541,926.18 and your OpEx will be $591,694.20, totaling $1,133,620.38, to *gross* $70k/year. Your profit ratio will be 6.18%, and the *only* ways to get that up are to reduce your CapEx or not pay for the 3.9GWh. This is if you start *today*. If you could even supply power to this cluster, you would also have the warmest house in the winter and procure bonus tinnitus! I can recalc for 5830s/6870s if you really want.