I've seen many people link to Edward Tufte's video on the iphone interface so I followed suit. Yes, he does a good job articulating some of the great design choices made by Apple and throws in some good suggestions, but he seems to make the assumption that the single point of interface design is to increase information density/resolution.
I disagree with his assessments on the stock and weather widgets. Yes, you could change them to present more data on the screen. But that has several consequences. The biggest thing is that more information requires more cognitive load. More is complex. More is slower. Wouldn't you be pissed if you just wanted to know what the temperature is tomorrow -- but you had to move the iphone close to you and squint to see it?
Please, let's not teach people to optimize interfaces by one single metric. Design is the art of balancing. You are not designing if you ignore the other end of the see-saw.
ps: If you are into this stuff I highly recommend reading and listing to Aza Raskin. IMHO, he'd win the "Sharpest, yet still practical" designer award. I was really wowed when I heard him say "the content is the interface" at the AJAX Experience. Watch and learn.