Xcode Project Icon files and Organiser Archives artwork
I was just able to figure out how to get both of these working correctly (icons without warnings and iTunesArtwork in the organizer window).
For all the icons, Xcode seems to prefer them at the root directory of the project. Then I add the icon files (iOS 5) entry:
Then I add the icon files entry with just the iTunesArtwork files (also located in the root of the project, no extension on these)
I don't think this part matters, but I did move them to the 'Supporting Files' group in Xcode: