How much of "bad UI" is design or usability?

When we talk about “usable” or “intuitive” interfaces, Apple devotees and the web app crowd (myself included) tend to bias toward the first-time user….
— 37signals on the TripLog/1040 iPhone app

So true. Web sites are heavily-skewed towards winning people over on first-impression, which puts a lot of importance on perceived simplicity and attractive graphic/UI design. But it also undervalues real usability vis-a-vis accessibility and task-completion, which the app’s author (a veteran Palm developer) spent a lot of time trying to explain in the comments regarding the look-and-feel of his first iPhone application. In the end, all of his principles were valid, they just weren’t styled well, or assembled Apple-y enough for the masses.

It will definitely be interesting to see how developers moving to the iPhone from other mobile platforms weather the transition going forward.

[Edited 11-07-2007] Not sure if this reviewer is being meta, but one of the app’s first reviews on the App Store itself is “This lacks all of the UI elegance that the iPhone has come to be known for. This belongs on a Palm Pilot.”