That was me. One latte plus $25 worth of food for two homeless guys outside. Turns out they didn't want any of it. I think I might've insulted them by bringing them food that they hadn't asked for. :/
This is a pretty great counterpoint to people who see something like this and immediately think of those who want to 'game the game'. Not that the exception proves the rule, but altruism does (in my opinion) beget altruism, good on you Sam.
It looks like things have died down. The steady state seems to be one where the balance is low and the transactions are small: http://dpaste.com/589113/ . That would imply that the card is currently being used as intended.
Looks like it only gets abused when there is a high balance that people can see on the twitter feed. A solution is to focus on coffee not money. "at least one coffee is available" or "buy someone a coffee, no coffee available" or "someone gave the gift of a coffee". Oh, FYI free coffee refills after purchase in shore.
The unfortunate thing about structuring the card in that manner is that: 1) it's not the way the card is programmed to work and 2)the experiment was to provide a vehicle for those who can't to benefit from those who can. The moment the individual the experiment as designed for would end the experiment; the inevitable end of buy one, give one.