Wow - love the concept and vision here. Were I such a person, I might dub this payments 2.0. This image on their home page gave me chills, though. http://a1.sqimg.com/static/6c1cc3c1ad109e13d0be182c75c470762... But that's likely only because I'm a half-paranoid security geek.
I seriously gotta wonder how the iPhone of some random person (which has various third party apps on it, etc.) is going to meet the kind of security requirements the card issuer cares about: http://en.wikipedia.org/wiki/Payment_Card_Industry_Data_Secu...
Also, most Windows PCs aren't PCI-DSS compliant but people still use them for online shopping and banking.