The install scripts currently assume that all developer tools are located in /Developer. This is true in Xcode 4.2, but starting with Xcode 4.3, the application is now delivered as a single application bundle via the OS X app store, and a number of additional tools like PackageMaker must be installed separately.

This is not critical, since there's no rush to switch tool or IDE versions in the official builds that I'm aware of, but those engineers starting on Lion will have problems setting up a full build since Xcode 4.2 is no longer available. Workarounds are available -- you have to symlink to get to PackageMaker and Rez and DeRez moved to /usr/bin, but it would be good to minimize the setup needed to build.