Remove trimmed version form preview screen?
Ah, the linked template.php override method (code below) does work but you need a sub theme for it to do so. 

/**
 * Override node preview to remove trimmed teaser version.
 */
function theme_node_preview($variables) {
  $node = $variables['node'];

  $output = '&lt;div class="preview"&gt;';

  $preview_trimmed_version = FALSE;

  $elements = node_view(clone $node, 'teaser');
  $trimmed = drupal_render($elements);
  $elements = node_view($node, 'full');
  $full = drupal_render($elements);

  // Do we need to preview trimmed version of post as well as full version?
  if ($trimmed != $full) {
   // drupal_set_message(t('The trimmed version of your post shows what your post looks like when promoted to the main page or when exported for syndication.&lt;span class="no-js"&gt; You can insert the delimiter "&amp;lt;!--break--&amp;gt;" (without the quotes) to fine-tune where your post gets split.&lt;/span&gt;'));
    //$output .= '&lt;h3&gt;' . t('Preview trimmed version') . '&lt;/h3&gt;';
    //$output .= $trimmed;
    //$output .= '&lt;h3&gt;' . t('Preview full version') . '&lt;/h3&gt;';
    $output .= $full;
  }
  else {
    $output .= $full;
  }
  $output .= "&lt;/div&gt;\n";

  return $output;
}


UPDATE this has stopped working for me. It seems the code doenst work properly with my zen template. 

UPDATE This code worked for me:

            /**
             * Returns HTML for a node preview for display during node creation and editing.
             *
             * @param $variables
             *   An associative array containing:
             *   - node: The node object which is being previewed.
             *
             * @ingroup themeable
             */
            function THEMENAME_node_preview($variables) {
              $node = $variables['node'];

              $output = '&lt;div class="preview"&gt;';

              $preview_trimmed_version = FALSE;

              $elements = node_view(clone $node, 'teaser');
              $trimmed = drupal_render($elements);
              $elements = node_view($node, 'full');
              $full = drupal_render($elements);

              // Do we need to preview trimmed version of post as well as full version?
              if ($trimmed != $full) {
               // drupal_set_message(t('The trimmed version of your post shows what your post looks like when promoted to the main page or when exported for syndication.&lt;span class="no-js"&gt; You can insert the delimiter "&amp;lt;!--break--&amp;gt;" (without the quotes) to fine-tune where your post gets split.&lt;/span&gt;'));
               // $output .= '&lt;h3&gt;' . t('Preview trimmed version') . '&lt;/h3&gt;';
               // $output .= $trimmed;
               // $output .= '&lt;h3&gt;' . t('Preview full version') . '&lt;/h3&gt;';
                $output .= $full;
              }
              else {
                $output .= $full;
              }
              $output .= "&lt;/div&gt;\n";

              return $output;
            }