[CoffeeDregs]

Two notes:

1) This can already be done using a simple stripe reader.

2) Coin can identify, investigate and proactively block anyone who has more than the average number of cards, so Coin actually seems well positioned to reduce fraud. Also, Coin could identify that multiple Coin cards have the same credit/whatever cards on them and, the next day, prompt you to swipe your card again to confirm. [Provided that Coin uploads suitable data to its servers...] In fact, using a Coin card could be a signal to fraudsters not to commit fraud against your card.

[joshfraser]

Yes, credit card duplicators have been available for a long time, but the average minimum-wage worker doesn't know that. This changes the game -- kinda like how how the prevalence of high quality camera phones changed the game for sexting. You could do it before, but it happens a lot more now that it's so convenient and the technology is available to the masses.

[vklj]

And by using the location of your phone, and the timing of the swipes, Coin can learn a lot about your shopping habits.

Not as much as the credit card company (e.g. not the amount of the purchase), but still quite a lot.

[praxeologist]

You have to take pictures of the cards. I assume it would work similarly to how I can take photos of checks to deposit them where, within some tolerance, you have the check/card inside of a "frame" allowing the check to be read. Maybe they can also sort of OCR the card name and make sure it matches your own.

[fragmede]

Additionally: simple stripe readers have been available for years now, and fit quite easily in one hand.

http://www.baltimoresun.com/media/photo/2011-08/64038442.jpg

[raybeorn]

Just because I am using coins hardware doesn't necessarily mean I need to use their software. And if it does catch on in the main stream, I doubt many people will check to see if it is your card if a check actually exists.