I think you could make a much cheaper and higher valued BTC miner farm without a computer. I'd look at some of the racks people are building for BTC'ing, some are small $40 boxes much like Raspberry Pi's, but stronger focused at the chore at hand. A rack of these little things are usually at least in groups of 12, so you're looking at about the same cost, but less power and a higher ability to mine than a pretty complicated computer...and sips power.
Remember, when you want money you have to keep upfront costs down and also maintain low costs through it's lifespan; and that goes for any investment. You might be losing money with a monthly power bill that really doesn't work out in the end vs. many other routes you can take up front. You'd be surprised what a computer costs to run when you want it to make money, find aliens, or cure cancer. I think I saved about $180 a month shutting all my folding stuff down and Bitcoin mining on a single computer may cost $15-18 a month. Over a year, how many coins will you get and what is it's value at that time vs. $180 a year spent on running the machine?
I know it's a big thing and the bitcoin economy has skyrocketed...but you buy low and sell high right? I bought a pizza with bitcoins back in college. You know what that's worth now? I think I ate a freaking $2,200 pizza. Probably more, but don't tell me...I'll puke. Anyway, there's a saturation of all economies and you can't just print more computers like you can money