In Xcode 4.3.2 you might also need to define the icons as pre-rendered.
Click on your project on the left, select your target, and under the Summary tab you'll see the App Icons, along with a "Prerendered"checkbox. Check this box and rerun your app.
If the icon hasnt changed yet, you might also need to delete and reinstall (rerun) the app on your device, or perhaps even restart the device, before the new icon is used.
