How does an end-user or developer easily separate the BSD-approved code
from the rest (GPL, etc.)?

Do they just remove the /usr/src/gnu directory? Or other directories?

Or is there some Makefile changes that can easily do it?

Do you have any examples of building a NetBSD system that results without
the BSD-incompatible code?

And where is this documented?

Thanks,

   Jeremy C. Reed
   http://www.reedmedia.net/