I made a calculation once, using difficulty, BTC/USD, power usage and power cost as input. Consider hardware cost as zero because for some who have mined for a long time, mined bitcoins have covered hardware cost.
Assume: BTC/USD = 120. 1200 MH/s for 2x 7970 cards. Power cost = $0.1/ kwh. Power usage = 650 Watt. Making less than $0.5 is no longer considered profitable.
Find breakeven difficulty.
Difficulty = approximately 34 million. So at 34 million difficulty, it's time to turn off the GPU miners.
what? your math is wrong as fuck
right now, it is easy to make 100 euro of profit in one month(0.13kWh/euro), with just two 7950, mining scrypt coin
aka gpu will survive for a year at least
for me asic are non-existent until they stop with this pre-order shit, and give us available products which are ready to ship