"Any new system or gadget has a learning curve, but where the iPhone differs is that the nature of traversing that curve is more fun than frustrating. You swipe and pinch and tap and shake your way to familiarity instead of pressing awkward buttons and navigating byzantine menu structures. You learn the iPhone by playing with it, which encourages interaction because humans are built to play"

Johnny Holland - It’s all about interaction  » Blog Archive  » The iPhone is Not Easy to Use: A New Direction for User Experience Design