I just finished reading an article from earlier this year by Jakob Nielsen on iPad usability. It's a decidedly old-school look at the device soon after its launch, but he has some valid points. I'll highlight two that resonated with me:
First, Nielsen highlights the potential return of sorts to the UI "Wild West," last seen after the introduction of HTML imagemap functionality. This is a state in which interaction designers make liberal use of the flexibility to make anything clickable, yielding a discontinuity in interaction model from app to app or site to site. One key method that interaction designers can use to indicate clickability--making an object look like a button--has been clouded somewhat by the prevalence of 3D elements throughout the standard iOS UI and within apps themselves. Further, critical parts of both apps and the OS (see the tab bar) are displayed as flat in spite of their clickability.
Second, Nielsen discusses the implications of inconsistent effects from UI actions:
In different apps, touching a picture could produce any of the following 5 results:
- Nothing happens
- Enlarging the picture
- Hyperlinking to a more detailed page about that item
- Flipping the image to reveal additional pictures in the same place (metaphorically, these new pictures are "on the back side" of the original picture)
- Popping up a set of navigation choices
To me, this has always seemed to be a side effect of the broader adoption of gestures in interfaces: what seems "natural" to a perfectly reasoned user-centered design effort will likely differ from what seems "natural" to at least a non-trivial subset of users. Gestural controls are by nature implicitly-defined; since there is no physical representation of an action (e.g. a button or hyperlink), each user must intuit what the developer coded as the correct action to accomplish a goal. Of course, there can be standards here (double-click to zoom in, pinch to zoom out), but in an application where zooming is not a core function, a designer will be hard-pressed to resist implementing double-click as some other fundamental action for the app. I think we'll get to consistency and predictability soon, but it's interesting to see how many inconsistencies are out there today. I still get confused from app to app on my iPhone after using the same things daily…
Anyway, here's the original summary. It links to a 93-page report!