Just for fun (as mining profitability calculators are not by any means the word of god, as it were)
The most expensive mining.thegenesisblock.com thinks you should be able to sell BFL minirig for is: BTC429.941
This would yield, they surmise, a lifetime profit of BTC0.000616
I don't think the network hash rate will increase exponentially as these calculators suggest.
You just cannot keep plugging new equipment to existing power network and expect them to work.
Even with these BFL minirigs you simply cannot run them at home anymore.
They need two 15A dedicated circuits and proper cooling. Professional hosting warehouse is what they need.
So expecting an exponential growth is probably a wrong assumption. But then again, I'm the seller so I'm biased.
Right now, they make
BTC6.4/day