Media Markt and Saturn are two businesses that I'd expect would take credit cards but they don't. Many restaurants (where you can spend more than €10 if you are more than one person, even here in Berlin) only accept cash. Most of the cheap Supermarkets don't take credit cards but will take EC (debit) cards, which I don't think Number26 offers - judging by going through their website. Nevertheless less, I applied for an invitation.

I don't know anything about the banking system in the US, but having moved to Germany from Britain four years ago, I thought the German system is archaic. When I moved, many online retailers wouldn't take credit cards or PayPal but you would have to transfer money to them from your account. Most everyone I know carry around large amounts of cash because if you are stuck without it, you will have to look for a cash machine that won't charge you. You can get cards that allow you to withdraw money without fees, I have one, but those are still rare.