I have seen some recent discussion about miner's break even price. However, your break even point is not solely a function of the BTC value.
Miners should calculate their break even Value/Difficulty (V/D) ratio. That can be calculated using the following equation (derivation below):
C - Cost in USD/KWh
E - Efficiency in MH/J [or (MH/s)/(Watt)]
V/D = 2.3861*10^-5 * C/E
Currently the V/D is about (8USD/BTC)/(1888786.705) = 4.23*10^-6. Since this number is so small, it is a little cumbersome for discussion. Therefore I purpose we divide it by 10^-7 for discussion. Therefore, the equation reduces to
V/D = 238.6 C/E [with * 10^-7 implied]
The current V/D is about 42.3 [with * 10^-7 implied]
For a point of comparison, I am mining at about 1070 MH/s using 500 W. My electricity cost is 8.6c per KWh. Therefore my V/D 2.3861*10^-5*(0.086)/(1070/500) = 9.6. Therefore things have to get much worse for it to be unprofitable [9.6*10^-7 * 1888786.705 = 1.81 USD/BTC].
I think that using the V/D for comparison will be more useful than the current discussion about everybody's BTC/USD break even point. The V/D provides a consistent value for comparison, since it does not change with the difficulty every two weeks.
What is everybody else's V/D? It would be interesting to see how it varies by region and GPU setup.
I have a 9.6 in Illinois with 3x5850.
Symbol - Description [units]
V - Value [USD/BTC]
D - Difficulty [Shares/Block]
C - Electricity Cost [USD/KWh]
H - Hash Rate [Hash/s]
U - Energy Use [Watts]
E - Efficiency [MH/J]
X - Expense [USD/s]
I - Income [USD/s]
X = U [Watts] * (1 KW / 1000 W) * C [USD/KWh] * (1 Hour / 3600 s)
X = UC/3.6e6 [USD/s]
I = H [Hash/s] / (D [Shares/Block] * 2^32 Hash/share) * 50 BTC/Block * V [USD/BTC]
I = 50HV/(2^32D) [USD/s]
X = I
UC/3.6e6 = 50HV/(2^32D)
=> V/D = 2^32 UC / (3.6e6*50*H)
E = 1e6 H / U
=> V/D = 2^32 C / (3.6e6*50*E*1e6)
V/D = 2.3861*10^-5 C/E