What the hell, here is my stab at this. It doesn't work when it comes across a unreadable object such as 'C:\System Volume Information', but that might be a issue in the Path::Class::Dir than my code.

#!perl

use strict;
use warnings;

use Path::Class; #file(), dir()
use Cwd; #getcwd()

my $start_dir = dir( $ARGV[0] || getcwd() );

#print "DEBUG: Scanning $start_dir\n";

$start_dir->recurse( callback => \&report_leaf_dirs );

sub report_leaf_dirs {

  my $object = shift;

  #print "DEBUG: processing $object\n";

  return unless $object->is_dir();

  # Test to see if we can read it
  unless( $object->open() ) {
    warn "Unable to open $object\n";
    return;
  }

  # Test for sub directories
  foreach my $child ( $object->children() ) {
    return if $child->is_dir();
  }

  print "$object\n";
}
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