just read in our local free paper about an "all you can eat" restaurant in Japan that fines diners if they leave as much as a single grain of rice on their plate... and the cash is given to charity
It'll teach people not to be greedy and take more than they need and all for a good cause
Unfortunately I think it's more likely to act as a challenge, 'all you can eat' makes a lot of people intent on eating as much as they possibly can anyway. I'd hate to be told I couldn't leave anything