@joolzg: I've got a watt meter connected to one computer with a 7970 and it consumes 300W.
The computer would be running 24-7 anyway but idling at ~80 watts.
That's 220 watts extra = 5.28 kW a day.

I pay about 0.15€/kW = 0.79€ a day
Puter mines ~3€ a day.
Which leaves a 2.2€ profit. Not much but an investment in an independent currency.

I really need to solve the heat problem if I'll be able to mine this summer though. I was hoping for a Jalapeno but once I'd get one if ever, difficulty would be too high so I cancelled my order a few days ago. (I just received the refund and made aboout 1 BTC from it btw. Exchange rates...).