Jakob Nielsen has been reviewing and critiquing web sites and computer programs for many moons. Today he's posted an interesting survey of iPad users and gleaned a few thoughts about the strengths and weaknesses of typical apps' user interfaces.
Swipe ambiguity plagued users when multiple items on the same screen could be swiped.Carousels often caused this usability problem in apps that also relied on swiping to move between pages. Many users couldn't turn the page because they swiped in the wrong spot. Their typical conclusion? The app is broken.
Many apps squeezed information into too-small areas, making it harder to recognize and manipulate. In a related problem, apps featured too much navigation. This design problem was so prevalent that it deserves its own acronym: TMN. While it's true that our seminar on navigation design covers 25 different navigation techniques, any given user interface should contain only a few. These two problems interact, because a larger number navigation options gives each one less space.
-Alertbox blog, May 23, 2011