Great post
http://www.reddit.com/r/Bitcoin/comments/1mgh0s/well_despite_all_the_talk_of_never_seeing_a_roi_i/cc91870[–]historian1111 66 points 14 hours ago
People need to STOP using fiat exchange rates to calculate mining profitability. Doesn't matter if you use USD/EUR/YEN/POUNDS.
Think about what you're actually doing when you buy a mining device. You are buying a machine that does one thing and one thing ONLY, it makes bitcoins. Infact, for all intents and purposes, it only makes a finite amount of bitcoins.
If you are smart, you can calculate how many bitcoins your miner is likely to ever make. If you buy a miner for 100BTC, and it only mines 90BTC, then you have lost 10BTC.
Now heres the trick that manufacturers do to rip off idiots. They have calculated that the miner will only make 90BTC, so instead of plugging it in and running it for a year or so, they try to sell you the miner for 100BTC! Not only do they get 10BTC more, but they get their return right away. (The time value of money is also valuable)
So instead of selling the miner to you at 100BTC, they just say '$10,000' (assuming the exchange rate was $100/btc). This tricks most people into trying to worry about what the future exchange rate is. But its actually irrelevant!
Why? Because with your $10,000 you could buy 100BTC right now on an exchange, instead of buying a miner that will only return 90BTC to you. So, you're effectively paying $10,000/90 = $111 per BTC instead of $100 per BTC. You just got ripped off.
When you buy a miner that does not ROI in BTC terms, you are basically paying a higher exchange rate then you can get today on MTGOX.
Another way to look at is, is imagine that I tell you to send me 100BTC or $10,000, and in return i'll give you 90BTC back. Only an idiot would say "don't worry, even though i got 90BTC back, i'll make up for it when the exchange rate goes up! " You're still missing out on 10BTC that you would have if you just bought on MTGOX!
