Coffee: A Social Experiment

I read a blog post yesterday about an interesting social experiment. Johnathan Stark loaded $30 onto a Starbucks card and then shared an image of the card online. Since July 7th, people have been using the card. At times, the value of the card goes to zero. However, more often than not, there is money on the card. Anyone can take the image of the card, go to Starbucks, and get a free coffee.
Something about this story struck me. It is an interesting social experiment in sharing and giving back. Anyone could go to Starbucks and buy $50 worth of coffee beans. However, if this were the case, there would never be money on the card. But, there is money on the card (you can keep track at http://mobile.twitter.com/jonathanscard). Over $3,600 has passed through the card. People are not just being greedy. People are adding value to the card!
So, what would you do? What would your students do? I would love to figure out a way to apply this experiment in a school setting. If you have an idea, let me know.