Jeremy Bower

 

Pinch Media:

For free [iPhone] applications, only about 20 percent of users return to use the app the first day after they download it, and then it quickly drops off from there. By 30 days out, less than 5 percent are using the app. The chart for paid apps shows a slightly steeper fall-off rate. So there is a very brief window of time to capture people’s attention and potential revenues.

John Gruber:

I’ll put forth one central, overriding guideline for iPhone UI design:

Figure out the absolute least you need to do to implement the idea, do just that, and then polish the hell out of the experience.