Now here's an interesting case involved Asda in Peterhead - apparently, due to a glitch in the store's computer system, large numbers of debit card transactions took several weeks to clear.
And, as a result, says the Aberdeen Press & Journal, customers have been sent overdrawn when the transactions eventually hit their account.
You could argue that it's the shoppers' fault, but one of the reasons people tend to use debit cards (including yours truly) is that it allows you to know how much is left in your account at any given stage.
The paper reports that Asda has apologised to customers and offered to pay any bank charges that result. One woman, the paper says, was charged more than 270 quid in overdraft fees.
It's enough to drive you into using a credit card - well, not quite...