Here's another way to look at the OP's investment. He could have spent $8000 on bitcoins. I'm sure they'll be $13 again this weekend, so I'll use that as the price.
8000/13 = 615
At 7 gigahash the OP should be mining around 3.5 bitcoins a day, at a power cost of at least .5 btc/day. Now assuming no difficulty increases we're talking 200 days to earn that many BTC.
Look at prices and difficulties right around the end of last year (200 days ago) to guestimate how likely it is your hardware will *ever* generate anywhere near 600 bitcoins over its lifetime. You've just bet 8000 dollars no ASIC of FPGA miners get introduced until well into next year, and the 7 series radeons won't be very good at mining -- both very poor bets.
Not to mention that he could sell those 615 bitcoins for 16 dollars within 1-3 days of buying them at 13 making him $1840 within a week. He could probably do this multiple times. If he bought again using all $9840 at 13 he would have 757 coins and could cash out at $12112 if it hit 16 again. Thus making more than he could ever hope to mine in the matter of 1-2 weeks.