When starting my iPhone application, I'm seeing both the status bar from Default.png and the OS's built-in status bar, instead of just seeing the OS's status bar. What have I done wrong?
R – see double status bars when starting the app
Resize your Default.png to exactly 320x480.
If your Default.png is exactly 320x480, it will be displayed full screen layered below (in z-order) the status bar. (This means the user will see the real status bar, not the Default.png one.)
But if your Default.png is some other size, the iPhone OS will scale it and display it positioned under the OS's status bar. (This means the user will see the real status bar at full size, and the Default.png one scaled.)
Note: Apple's documentation specifically states the 320x480 size, leaving undocumented that it works at all with other image sizes, let alone this scaling behavior. So you probably shouldn't rely on this.