That's 12kWh at let's say a $0.12/kWh residential electric rate ( http://www.bitcoinminer.com/post/2361900289/where-to-mine-el... ) that's about $1.44 per day for your electricity.
A 5970 hashes at just under 600 Mhash/s, per http://en.bitcoin.it/wiki/Mining_hardware_comparison so punch that 600000 number in as khps here: http://www.alloscomp.com/bitcoin/calculator.php
and it shows that at the current difficulty level, you should generate 50 BTC about every 3 days and 29 minutes.
So in a 24 hour period you get about 16.55 BTC per day. Converting that 16.55 BTC to USD: http://bitcoin.1t2l.net/widget/?from=BTC shows you earn about $15.28 per day with a rig holding a single 5970.
Then to send those BTCs to your PayPal, you use http://coincard.ndrix.com (starting again monday morning) and you lose 3% doing that conversion so you end up with $14.82 in revenue per day. Subtract the $1.44 in electricity that nets you $13.38 a day. If that were to hold, you'ld have the card paid off in well under two months.
That said, ... difficulty is rising (fast! ... http://bitcoin.sipa.be/speed.png ). If the BTC/USD exchange rises more ( it's had quite a run http://bitcoincharts.com/charts/mtgoxUSD#rg60ztgSzm1g10zm2g2... ), then that payout might continue at these levels. Otherwise, the payout from mining will decrease.