Custom Formatter to display published on date as defined by the "Publication Date" module. (Use this gist as CTools Import Code)

import.php

$formatter = new stdClass();
$formatter->disabled = FALSE; /* Edit this to true to make a default formatter disabled initially */
$formatter->api_version = 2;
$formatter->name = 'published_date';
$formatter->label = 'Published Date';
$formatter->description = 'Displays the date that the node was published.';
$formatter->mode = 'php';
$formatter->field_types = 'list_boolean';
$formatter->code = 'if ($variables[\'#items\'][0][\'value\']) {
  if (isset($variables[\'#object\']->published_at)) {
    return date(\'m.d.Y\', $variables[\'#object\']->published_at);
  }
  else {
    return \'<p>Missing plugin. Please install the `publication_date` module or select a different formatter for the \' . $variables[\'#field\'][\'field_name\'] . \' field.</p>\';
  }
}
else {
  return false;
}';
$formatter->fapi = '';