We have many many customers on postagram and popbooth that don't have a problem with entering a credit card. This is THE way that Apple wants developers to charge for physical goods - see item 11.3 on these guidelines http://appadvice.com/appnn/2010/09/apples-app-store-review-g... (the actual guidelines are behind a login for developers). So given these constraints, we believe this is a very seemless flow - and our customers agree.
