I've spent another few hours crunching numbers to try to work out some of the current economics of bitcoin mining as a whole. I've been interested in how much money has been generated by mining and how much has to be spent on mining hardware. I also took a guess at when the next fixed block reward will halve next time and what the current peak hashing rate might look like (assuming the best current 28 nm ASICs).
If anyone is interested then you can find the write-up at:
http://hashingit.com/11-the-rewards-for-a-bitcoin-minerIt looks like you are completely omitting the added tax complexities and cost associated with US based mining, thus for me the write-up is incomplete and doesn't seem relevant for the times. Just being honest, my opinion.
I guess the interesting question is just what percentage of the mining is taking place in the US? Up to now there hasn't really been a huge tax complication and it will be interesting to see what effect that has. It's difficult to estimate the impact given a lack of any historical data.
For anyone mining as a commercial enterprise then I would expect that if any income is being reinvested in mining equipment then the tax liabilities will be marginal - it's certainly there for any individuals though.
That's the first half of the problem, US complications. I believe the worse has yet to come, as since China and USA are cracking down on BTC (regulating would be a better word here), I believe more countries will too as well as many countries look at economic superpowers and gauge on what they should do based on what USA and China did. So I believe that US percentage of miners (which I believe is fairly high, as their pretty lenient right now, even with tax guidelines) is irrelevant, as if other countries follow suit... Its not just US tax guidelines you'll have to go by, its by xxx countries.