I don't have a use for Coin - I have few cards, but the product reminds me of a quote often attributed to Henry Ford, "If I had asked people what they wanted, they would have said faster horses." While I think it's great for people who have many cards, and there are probably tons of customers like that, it doesn't seem that interesting from a tech point of view.
The tech point of view is the most interesting! They made a reprogrammable credit card that's the same thickness as a credit card. That's impressive tech whatever your opinion of the utility.
