Jakob Nielsen’s Alertbox: iPad Usability: First Findings From User Testing

iPad apps are inconsistent and have low feature discoverability, with frequent user errors due to accidental gestures. An overly strong print metaphor and weird interaction styles cause further usability problems.

Indeed, one finding from our study is that the tab bar at the bottom of the screen works much worse on iPad than on iPhone. On the small phone, users are likely to notice the muted icons at the bottom of the screen, even if their attention is on content in the middle of the screen. But the iPad’s much bigger screen means that users are typically directing their gaze far from the tab bar and they ignore (and forget) those buttons.