I'm getting between 750 to 800 Mhash/s on my 2 6970's. They are clocked to 940. You'll need to bump up the voltage to +5% and use the -v -w 128 flags (poclbm) or else you'll only get 600 Mhas/s (~300 per card). I'm doing the mining in windows using the poclbm miner.

At the current difficulty level, they are producing roughly 1 BC per day (slightly less). At current BC prices that means I can get about $400 per month.

My computer uses 650 Watts when mining. That's about $70/month in added electricity without factoring in added cooling (i.e., AC) costs.

IMO it's also prudent to assume there will be downtime on your computer and the mining pool. I'm using an adjustment factor of 0.9.

So my current back of the envelope, conservative estimate is to clear $250 / month. The big question is how fast will the difficulty increase and what will the market prices do? It's very likely that the monthly return will decrease.

If you bought your computer and/or cards for another reason (i.e. gaming) then you can definitely make some money mining for BC's. If you bought your setup for personal use (i.e. gaming) and mining, then you can definitely recoup some of your initial investment. If you're looking to break even or turn a profit....that seems less certain.

Hope this helps. I'm interested in any feedback to my comments.

Matt