As an aside: Each person should do their own research and calculations to decide if purchasing miners is right for them. That being said, the numbers I have run are based on a very aggressive difficulty ramp up, and show the units will be unprofitable after 9-10 months. That being said, in order to maintain the exponential increase in difficulty, $26 million dollars worth of hardware would need to be introduced in month 3, $54 million in month 5, $110 million in month 7, and so on. This assumes .5btc per gh/s, and there are companies slated to produce miners at a .2.