One of the ways you can tell that a piece of UI design really works is when you start trying to use it in other apps. A great example of this: Mr. Reader’s navigation buttons:
Those up, down and close buttons at the side aren’t there all the time. In fact, you have to slide your finger in from the edge of the screen to show it, and it’s your finger is positioned automatically over the “down” button. You have to hold and slide up or down to use one of the other buttons: if you lift your finger, the buttons disappear.
The nice thing is that you can do this from any part of the screen edge, so it doesn’t matter where your finger starts. I usually use my thumb, as I’m holding the iPad in portrait orientation.
It’s a lovely user interface device: hidden, yet easy to find and simple to understand. And it’s one of the things that makes Mr. Reader my favourite news reader on the iPad.