The "quids" are cute, but I think they're missing the fact that loose change of any kind, even with rounded corners, presents a hazard in a microgravity environment. They need an information storage method that can hold up to electromagnetic flux and cosmic rays, with suitable encryption to hold financial information such as a credit limit. They're going to have to exchange information with a banking system, but it needn't be in real-time.
Regarding Yvan's request for a picture in black, I think he wants to see the Kindle mock-up photoshopped to seem to be made of black plastic. The color is quite likely to change, since that color is the basic color of prototyping plastic (someone pointed that out in one of the early Kindle threads). I'd expect to see some kind of customizable "skin," actually, if they want to go the iPod marketing route.