Depends on your definition of 'effective'. If you're writing for readability and maintainability, I would say that an effective Perl script isn't obfuscated at all. If you're wanting to take advantage of some efficiency tricks via map and complex data structures (via references), your code becomes slightly harder to read. If you're making use of aliasing and other "magic", things become harder still, but with ample documentation and consistent style, none of this has to appear obfuscated.