Not sure how many people use this plugin but 5 reported it not working in WP 3.0. The author hasn't updated it and seeing as my client needed this functionality, I was able to get it working in WP 3.0.
Reference: http://wordpress.org/extend/plugins/map-categories-to-pages/
Add the following to map-categories-to-pages.php:
function create_page_taxonomy() {
register_taxonomy('category', 'page', array(
'hierarchical' => true,
'label' => __('Categories'),
'singular_label' => __('Category'),
'show_ui' => true,
'query_var' => true,
'rewrite' => true
));
}
add_action('init', 'create_page_taxonomy');
Comment this line in map-categories-to-pages.php:
//add_action('admin_menu', 'add_category_box_on_page');