Document where nid entries are pointing to

Not sure I'm comfortable with that being there by default - makes a few assumptions that could lead to problems (like values for a nid field being a valid node id), and the output is a bit anti-drupal (are you a perl programmer??). Perhaps I will provide a hook so this can be done another way that is configurable. I also think in a majority of use cases the 'nid' values are completely misleading, and any references will be inaccurate on the destination site, so this might lead people to try and read the export code and subsequently get the wrong idea.

<?php

    foreach ($var as $key => $value) {
      $code .= $tab ."  '". $key ."' => ".node_export_node_encode($value, $iteration).",\n";
    }

?>

could become

<?php

    foreach ($var as $key => $value) {
      $out = $tab ."  '". $key ."' => ".node_export_node_encode($value, $iteration).",\n";
      $code .= drupal_alter('node_export_node_encode', $out, $tab, $key, $value, $iteration);
    }

?>

and then you do

<?php

function YOURMODULE_node_export_node_encode_alter(&$out, $tab, $key, $value, $iteration) {
  if (($key == 'nid') && $node = node_load($value)) {
     $out = $tab ."  '". $key ."' => ".node_export_node_encode($value, $iteration).',';
     $out .= "// '".$node->title."'";
     $out .= "\n";
  }
}

?>

Will think about it some more.

I've added the hook into the module. Hopefully this is satisfactory so you can change each array element to add your own output.