Another detail that Apple got right is the speed of the zoom. To be absolutely true to the real-world metaphor, the content underneath each finger should remain static relative to the finger. That is, if you put one finger down on the top right corner of an image, and the other on the bottom left corner, and then spread your fingers apart, they would still be over the corners of the image. In iPhone Safari, the zoom is actually slightly slower than this, meaning that you have to move your fingers a little bit further apart to achieve the same level of zoom — but it feels just right.

I’d guess that the hardware is the major factor here, but it still feels like there is some kind of software heuristic at work. It’s easy to take this for granted, but given my experience with various multi-touch interfaces, it’s actually a remarkable achievement that tapping links on an iPhone is as precise as it is.