What makes me sad is the severe case of analogy fever going around. It's not just this situation, it's everywhere; when people hit a novel ethical challenge it's like it's too hard to confront it on its own terms, and it has to be dragged back down into being "just like" something less interesting. The world is changing in fascinating ways with brand new ideas and challenges to understand, and we're punting to tradition instead of doing them justice.
Well, you know what? Piracy isn't "just like" stealing, nor is it "just like" swapping tapes was in the 80s. Wikileaks isn't "just like" publishing someone's diary, nor is it "just like" the NYT publishing the pentagon papers. And this isn't "just like" Robin Hood, or stealing out of a collection plate, or totalitarianism encroaching on liberty, or a clever publicity stunt, or black hat hacking, or the tragedy of the commons or anything else. It's just... well, it's just like the Jonathan's Card case of 2011.
Analogies aside, did Sam Odio do the wrong thing? I think there are a few important aspects to consider:
What should the donors have reasonably expected would happen with their money and how firm a moral hold do they have on that expectation? I've seen a few people argue that they were essentially throwing the money out the window, but I'm not sure how well that applies. The Starbucks card is more attractive because it's more restricted. Nobody could use it to buy shoes or pay down their mortgage. It was intended for coffee, and I think the people donating expected it to be used for coffee.
So did he wrong the people who donated money? By that definition, yes - but our society tolerates a lot of different kinds of wrong. It's wrong to lie and wrong to stab someone, but only one of those is illegal. If people donate money intending it to be used for charitable coffee, and you use it for a different charitable end, how bad is that? At least, less bad than buying an iPad, more bad than using it for its intended purpose. It obeys the large-scale "paying it forward" end if not the particular means.
The act being wrong from the perspective of the donors doesn't mean it needs to be wrong for everyone, though. Sometimes you can do bad and good in the same action - feeding Ethiopian orphans surely must, by any measure, do more good than giving people coffee. How much bad is justified by how much good? I'm certain that everyone has an answer in them, and probably an uncomfortable one to think about too hard. For me, I think this makes it over the line as enough good to be worth it, but I'm not sure it would if I were more invested in the experiment.
There is an interesting sidenote that I think hasn't been addressed much. Would the reaction have been as bad if he'd bought $600 worth of Starbucks food and given it to homeless people? I suspect not. To me, that suggests that the actual end was less important to most donors than the means. That is, it wasn't a charity effort with a communal coffee card as a side-effect, it was a communal coffee card experiment with charity as a side-effect. Or perhaps the order of those preferences indicates where you stand on the morality of the act.