Good deal. Once you add that functionality you should get websites to offer the user plums in exchange for giving them a slice of the pie. Sites like K5 and Fark and Slashdot already offer plums-for-money, so if you could make it easier for more sites to do this it would seem to be quite viral.

Edit: I think the idea of donating in real time would be most rewarding satisficers. The problem is that early adopters, almost by definition, are rarely satisficers.