This is a programming question! Read on before you vote to close!

According to Apple, iPhone 4 has a new screen resolution:

3.5-inch (diagonal) widescreen Multi-Touch display
960-by-640-pixel resolution at 326 ppi

This little detail affects our apps in a heavy way. Most of the demo apps on the net have one thing in common: They position views in the believe that the screen has a fixed size of 320 x 480 pixels. So what most -if not all- developers do is: They designed everything in such a way, that a touchable area is -for example- 50 x 50 pixels big. Just enough to tap it. Things have been positioned relative to the upper left, to reach a specific position on screen - let's say the center, or somewhere at the bottom.

Edit: It seems Apple has integrated an switch that allows to tell if an app is highRes or not. Nice.

When we develop high-resolution apps, probably they won't work on older devices. And if they did, they would suffer a lot from 4-times the size of any image, having to scale them down in memory.

This is community wiki. Just add anything that you think is relevant to this huge problem (constant screen res was one of the main reasons why I didn't go for Android!!).