I preordered one of these last week. I'm pretty stoked about it.
For some things in the thread:
If your coin is stolen, it deactivates. It does so by not being able to communicate to the phone after a period of time. They're undecided at this point, looks like 10m tops, but it may be user configurable. Basically, if someone steals coin, ten minutes later it's useless. This is great as opposed to a regular card, where you have to call in and cancel it and get a new one issued.
It looks like there may be some kind of approval process for adding cards to the coin. Not sure how it works yet, no details, but you have to swipe the card and take a picture of the front and the back. It could possibly use some kind of OCR on the image to determine the name printed on the card or it might require a manual approval by the Coin staff. No details yet, but they seem pretty confident you won't be able to add cards to Coin that aren't you're, preventing servers in restaurants from just swiping your card to steal it.
The biggest wonder I have right now, is how to stop someone at a restaurant from switching your card on the Coin. Let's say I put the Coin in the little wallet they give you and, on it's way to the cash register, the button gets pressed and now it's on the card you didn't intend to pay with. I hope there's some sort of lock as I have one card I use 90% of the time.
I think it's a pretty solid idea, but uploading your card info via an app isn't going to appeal to most. If there was a way to directly and locally upload my cards workout network use then I honestly might give it a try. I don't really see any bigger security issue than any other card, and honestly it might be better because the card number can't be seen.
Unsure yet if it requires a network connection. I know you have to have the app, then swipe your cards and take their pictures in the app, but after that it just communicates to the Coin over Bluetooth. Unsure if you actually need a network connection at that point, but the card will have to be in contact to the phone via Bluetooth.
Very very skeptical with the entire smartphone payment thing. Not only do thieves now get your "wallet", they get your $500 phone.
With current NFC payment techs, they time out after a period of time. This means you have to put in your PIN every X minutes in order to reauthorize transactions. Same concept with the Coin, checking in over BT every so often.