I bought just under $1000 of cards and cases and I get 1100Mh/s. I get about 5BTC/day at BTCMine. From what I figure, difficulty should double every 23 days. Every difficulty increase is at about 140% and happens every 10 days. If the next difficulty increase is in 5 days from now,... I'll have :
50 for the next 5 days (and previous 5) ($350)
35 for the next 10, ($245)
25 for the next 10, ($175)
17 for the next 10, ($119)
12 for the next 10, ($84)
_8 for the next 10, ($56)
$1029 will take 60 days. I estimate power cost to be $2.00 per day including A/C. So, if I were starting right now and prices would remain at 7 USD/BTC, then it would take me about 2 months to break even.
Does this all look right?
$2 for power a day seems little low, the rest is sound. You can expect the difficulty rises to calm down if the price doesn't go up 2 weeks from now.