I'd think that Duff's device is never useful in Perl.

It is certainly not useful in my obfu, I could have finished the obfu like this as well:

tie @b, &^Px$^P;
# without duff's device I can copy array very efficently
push @b,$_ for@a;
# oh, I nearly forgot magical subs, so here they are
sub DESTROY { }
sub AUTOLOAD {
        ($#, %c)= qw(%c $#);
        print $_[1];
        bless [];
        }
__END__
[download]

This would be as good as the original, just not as obfuscated.