This is not what the "Pay it forward" concept is all about. Hipsters helping hipsters is fucking moronic, people do this at pubs all over Europe and no one there feels good about themselves for doing it. It's simply a way of keeping tabs and making ordering drinks way less awkward. Do something nice for a stranger in need, spend some time to take interest and actually do something of worth instead of covering some random person's coffee.

Edit:

I ran all this by economist Russ Roberts, host of the great EconTalk podcast and author of the upcoming book How Adam Smith Can Change Your Life. He agreed, and even took issue with the premise of the chain. "The whole idea that the person behind me at a Starbucks needs to be comped is a strange idea," he says. "Nobody’s in duress here. The real idea of 'pay it forward' is, I break down on a snowy night, I lose control of my car and end up in a ditch, four strangers come along and push me out. Then I’m driving along and I see someone else in a ditch, and I pull over and help them. That’s paying it forward. You made a sacrifice. Paying it forward for someone at Starbucks who’s already got $5 in their hand? That strikes me as a bizarre form of 'pay it forward.'"

This.