I think this is a really nice feature request.. I’m was actually looking for this and was not able to find anything..

Thanks

WordPress 2.9.1

Create admin-script.js in theme folder and edit:

jQuery(document).ready(function($){
  $('.cat-checklist')
    .prepend(
      '<li><label class="selectit"><input value="1" type="checkbox" name="remove_categories" id="remove_categories"/> Remove Checked Categories</label></li>'
    );
});

functions.php:

function my_enqueue() {
  wp_enqueue_script('my_admin_script', get_bloginfo('template_url') . '/admin-script.js', array('jquery'), false, true);
}
add_action('admin_init', 'my_enqueue');

function my_bulk_edit($action, $result){
  if('bulk-posts' == $action && isset($_GET['remove_categories']) && isset($_GET['post_category'])){
    if(($_GET['action'] != -1 || $_GET['action2'] != -1 ) && ( isset($_GET['post']) || isset($_GET['ids']))){
      $post_ids = isset($_GET['post']) ? array_map( 'intval', (array) $_GET['post'] ) : explode(',', $_GET['ids']);
      $doaction = ($_GET['action'] != -1) ? $_GET['action'] : $_GET['action2'];
    }
    if('edit' == $doaction){
      if(isset($_GET['post_type']) && 'page' == $_GET['post_type']){
        if(! current_user_can('edit_pages'))
          wp_die( __('You are not allowed to edit pages.'));
      } else {
        if(! current_user_can( 'edit_posts' ))
          wp_die( __('You are not allowed to edit posts.'));
      }

      $post_IDs = array_map('intval', (array) $_GET['post']);
      if(is_array($_GET['post_category']) && ! empty($_GET['post_category'])){
        $remove_cats = array_map('absint', $_GET['post_category']);
        unset($_GET['post_category']);
        foreach($post_IDs as $post_ID){
          if(wp_check_post_lock($post_ID)) continue;
          $cats = (array) wp_get_post_categories($post_ID);
          $post_data['post_category'] = array_diff($cats, $remove_cats);
          $post_data['ID'] = $post_ID;
          wp_update_post($post_data);
        }
      }
    }
  }
}
add_action('check_admin_referer', 'my_bulk_edit', 10, 2);

Check ‘Remove Checked Categories’ and categories you want to remove!

Frelling brilliant. Thank you – You saved be about an hour and a half of combing thru posts!

Takes me to a blank white page after I hit “Update”, but when I go back to the post listing & refreshed the page, I see that it did do it’s job. Thanks for the script!