Does nobody care that this is an obvious ponzi?
There is always a risk that this is a ponzi. That's why you shouldn't put all of your eggs in one basket.
With that being said, I found a competitor, located in the UK, with the same business model and similar prices. Their mines are located in the UK, USA, and South America. They list their company name and address.
It shows that either:
1. PBmining has a viable business model and is not necessarily a ponzi
or
2. There are 2 rival ponzi schemes competing for your BTC.
I think the bigger risk is whether the difficulty increases will erode any profits. The next increase is projected to be around 19% in 7 days. This calendar year, the average increase has been 16.15%. Some customers have recently reported breaking even.
Running the historical numbers, if you purchased a 1,000 GH/s contract on January 24th, you would have paid 16BTC. Your milestone dates would have been:
25% Feb 11
50% Mar 8
75% Apr 16
100% (break-even) Jul 1
107% Aug 10
Using the same difficulty increases and shifting the dates, if you purchase a 1,000 GH/s contract on August 8th, 2014, you pay 2.9BTC. Your milestone dates are:
25% Sep 10
50% Nov 13
70% Apr 30
72.5% Sep 6
No break-even
Hmmm, I hope we have some single digit difficulty increases coming up. As the difficulty gets higher, it will take an increasing amount of equipment to sustain the double digit difficulty increases.