I've known a lot of people who pay for things using their debit cards whenever possible. They feel weird carrying around large sums of money, presumably because they fear a criminal with X-ray eyes will see the wad of cash right through their purse/coat/wallet/etc. and target them for a mugging.
But as often as not, these same people own a shiny new top-of-the-line cell phone that they'll take out and use anywhere, anytime, without a thought.
Mind you, I've never heard of anyone getting mugged for their cell phone (or laptop, or iPod), so maybe there's a method to this madness. To me, though, it's an amusing contradiction to be afraid of carrying $100 cash in your pocket when you regularly brandish a $400 phone in your hand.