the app store botched its installation of Xcode 4.1 (it turned claimed it was 4.0 but the app store claimed 4.1 was installed). So I deleted the /Developer folder thinking this would let me reinstall a clean Xcode 4.1.
The app store still thinks Xcode 4.1 is installed and will not download or reinstall any version of Xcode. How do I force install Xcode 4.1?