I ran cgminer on a nvidia card last week and the payout after 30 hours was like 0.00004 btc or something like that.
You would probably get more bitcoins if you put a sign and a cup on the sidewalk saying "Give me some money please", and buy bitcoins for the profit.
...or just sell the cup right away
You made my day.
I guess the New York beggars will demand donations in bitcoins now