Well.. Here's what I've done out of this discussion thread.
It's a little bit mischievious.. but.. it's ok for now..

Let's imagine script.pl

#!/usr/bin/perl
use strict;
use Getopt::Std::Strict 'dh';

INIT {
   $SIG{__WARN__} = 
      $opt_d ? sub { warn(" # @_\n") } : sub { 1 };
   $opt_h and print usage() and exit;
}

warn "Hi there. I am stuff, very interersting stuff.";

sub usage { "-d flag to see interesting stuff\n" }
[download]

So essentially, I can code debug into an existing class or script, that simply turns warnings off or on via something like an option flag or a class DEBUG variable. Very sexy.

Back to your point.

Yes, I have to hand it to you .. "$DEBUG and ..." is not as clear as "... if $DEBUG". To the normal human being. I think I've been using and or ? : so much that you just start to think like the interpreter a little bit so.. it becomes part of your language at the time. I feel no difference between "x and y" and "y if x". Odd.