I am using my GTX 480 for mining and it's crunching at about 106 Mhash/s. Is it better for me to be on Pay-Per-Share or Proportional payout?
I would sell it and replace it with an ATI.
You are using roughly ~500w @ full load. With 80% PSU efficiency you're pulling 600w from the wall. 600w/hour * 24 hours/day * 30 days = 432 Kwh and at $0.10/Kwh, you would be paying $43.20 a month in electricity and pull in about 57.5 BTC per month or $52.33 a month at current difficulty and current Mt.Gox market price, netting $9.13/mo.
I don't like using ATI cards, their driver support for Linux is not very good.