Jakob Nielsen on iPad. He has the results of some testing he did on the iPad interface.
iPad by byrion
Most of the insights relate to app design and not the iPad itself. In other words, most of the usability is within the app designer’s control.
To exacerbate the problem, once they do figure out how something works, users can’t transfer their skills from one app to the next. Each application has a completely different UI for similar features.
