We've had some discussion of various styles of building paths to scons (some initiated by my questions as I learn more), so I thought I'd add a piece of information I discovered through experimentation:
when a path is constructed to build for environment variable handling (help, default value, etc), the scons shortcut of # does not work. If you want to build a path to pass to an Add(PathVariable(...)) call, by default the path you give will be checked for existence - there are also options to change the check but no need to go into details. That check does not understand paths which begin with #, you have to give those as fully qualified paths.
