Bitcoin mining doesn't require memory bandwidth. Dropping memory speed to 300mhz, and maintaining 1150mhz overclocks at 1.08V average (1.175V peak) results in a GPU power usage of ~170W per card. Also, the value of each bitcoin has increased from $5-6 to $12 since January. The electricity cost for me varies from 6.5 ¢/kWh Lowest Price (Off-peak), 10.0 ¢/kWh Mid Price (Mid-peak) to 11.7 ¢/kWh Highest Price (On-peak).
Gaming 2-3 hours a day, mining 20-21 hours a day for almost a year.
Each 7970 @1150mhz generates ~ $80 bitcoins a month. 3 such GPUs then earn $240 a month, every month for 10 months so far.
That's ~$2,400 in bitcoins earned - $520 in electricity costs (510W for the 3 cards + 150W system @ highest electricity rate of 12 ¢/kWh for the worst case scenario x 21 hours a day x 310 days = ).
So ya, it's more than $1,600 in profits so far.
Dividebyzero,
retail launch 9 January, 2012 ---> it's been almost 10 months. Jan 9 to Sept 23 is not 8.5 months, but 9.5 months. Keep in mind, every month the 3x 7970s continue to make $240 in bitcoins, so another $240 in October, $240 in November too. They have already paid for themselves off fully.