Jakob Nielsen on iPad Usability

About the iPad's usability, Jakob Nielsen writes:

iPad UIs suffer under a triple threat that causes significant user confusion:

• Low discoverability: The UI is mostly hidden within the etched-glass aesthetic without perceived affordances.
• Low memorability: Gestures are inherently ephemeral and difficult to learn when they're not employed consistently across apps; wider reliance on generic commands would help.
• Accidental activation: This occurs when users touch things by mistake or make a gesture that unexpectedly initiates a feature.

When you combine these three usability problems, the resulting user experience is frequently one of not knowing what happened or how to replicate a certain action to achieve the same result again. Worse yet, people don't know how to revert to the previous state because there's no consistent undo feature to provide an escape hatch like the Web's Back button.

Undo is probably one of the most obvious usability problems with the iPhone and iPad. Shaking just isn't an intuitive gesture. You won't find it by accident or if you're looking for an undo feature, and there is no indication telling you which applications support it. In addition to that, shaking an iPad is not really a feasible user interface for anything.

I think there needs to be some standard, obvious way for iPhone OS applications to implement undo.