iOS 4 has an annoying bug for web app developers. If you use the
apple-mobile-web-app-capable feature to indicate that your site should launch as it’s own app rather than open in Safari, the OS creates a low-resolution version of your apple-touch-icon on the home screen:
The app on the right uses
apple-mobile-web-app-capable. The app on the left doesn’t. They were both generated from the same image.
Update: Finally fixed in iOS 4.1!