Actually on a local supermarket that I frequent to it takes about 30-60 seconds to complete a payment with a CC, really slow and by the time it finishes, a huge line has formed. With Bitcoin, if the supermarket provides their own free Wi-Fi, to which their own bitcoind is connected to, it will make the transaction way faster than a CC and best part, you don't need to wait for change, you pay the exact amount and just leave.