Re: www.lunamine.com - 0.0025 BTC/GHs mining contracts | On-demand withdrawals
The one thing I will say for PBMining is it is much better ran then lunamine was.
I guess that's self-evident. One is still in business, while the other suddenly disappeared.(However I still think they are both scams.) 
Just because we don't understand a business model doesn't automatically make it a scam. If I understand you correctly, you think that PBmining.com does not have a sustainable business model. Since it is not sustainable, it will eventually fail. The solution is to not invest if you think that will be the outcome.Anyway, the numbers still don't work in reality, because you can't buy power cheap enough, even at .5 W/GH for 5 years. One year, probably, two years it is iffy.
In reality, the cost of maintaining 1GH today is much more expensive than it will be one year from now and beyond. For example, one year ago, I bought a miner that cost approximately $85/GH and used 6W/GH. The $/GH and W/GH have dropped dramatically over the past year. I believe the business model assumes that we will have future efficiency improvements. It is these improvements that are the key to success. If these assumptions are wrong, then the business will fail. Because the development of mining equipment is highly competitive, I feel safe in predicting that in one year $/GH will be 0.30USD/GH or less and that power requirements will be 0.25W/GH or less.