[..]
Let's say that I did purchase one, however. At the current network difficulty and BTC exchange rate, that S5 would expect to make ~$3.25 a day before power costs. ROI would be ~123 days. Using a very conservative network difficulty adjustment value of 2%, we're up to ~136 days. That right there should have convinced me not to purchase one in the first place... and I assumed free power in my numbers.
That's lack of enterpreneurism...
Common business reaches ROI 2-3 years after initial investment.
We were (are?) seeing month-scale ROIs because of the highly speculative price of bitcoin.
If (when) bitcoin becomes more mainstream, expect ROI in a year or two... not less