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Give a penny, take a penny - that's the concept behind Jonathan Stark's new "experiment in social sharing." He has put a picture of his Starbucks card online so that anyone in the world can use his account to purchase a cup of coffee. Just save the photo on your smartphone, go to your local Starbucks, and scan the barcode. Simple as that. You'll have a free cup of piping hot coffee.

A Harvard University study built around an innovative economic game indicates that, at least for our younger selves, the desire for equity often trumps the urge to maximize rewards.