Hide WordPress' Categories widget on certain pages

hide_cats_widget.php

<?php
/*
Plugin Name: Hide Categories Listing
Plugin URI: http://tarskitheme.com/
Description: Hide the Categories widget on certain pages.
Author: Benedict Eastaugh
Version: 1.0
Author URI: http://extralogical.net/
*/

function maybe_hide_categories_widgets($sidebars) {
  if (!(is_page() || is_single())) return $sidebars;
  
  // Add page IDs to this list, e.g.
  // $hide_categories_on = array(1, 4, 9);
  $hide_categories_on = array();
  
  if (in_array(get_the_ID(), $hide_categories_on)
  || get_post_meta(get_the_ID(), 'hide_categories', true))
    foreach($sidebars as $id => $sidebar)
      foreach($sidebar as $i => $widget)
        if (strpos($widget, "categories-") === 0)
          unset($sidebars[$id][$i]);
  
  return $sidebars;
}

add_filter('sidebars_widgets', 'maybe_hide_categories_widgets');

?>