concise

I managed it by adding the following to functions.php, but would go better in a plugin (but really WP should have Visibility: public, password, private & hidden.

/*
 * from brickbrigade's code at http://wordpress.org/support/topic/get_post-query-where-posts-dont-have-a-specific-meta_key-1
 */
add_filter('query_vars', 'metakey_queryvars' );
function metakey_queryvars( $qvars )
{
  $qvars[] = 'not_meta_key';
  return $qvars;
}

add_filter('posts_where', 'metakey_where' );
function metakey_where( $where )
{
    global $wp_query;
    global $wpdb;

    if( isset( $wp_query->query_vars['not_meta_key'] )) {
       $where .= $wpdb->prepare(" AND $wpdb->posts.ID NOT IN ( SELECT post_id FROM $wpdb->postmeta WHERE ($wpdb->postmeta.post_id = $wpdb->posts.ID) AND meta_key = %s) ", $wp_query->query_vars['not_meta_key']);
    }
    return $where;
}

/*
 * variation of jamesstiff's code at http://wordpress.org/support/topic/excluding-pages-from-search-results
 */
function mySearchFilter($query) {
if ($query->is_search) {
$query->set('not_meta_key', 'hide');
}
return $query;
}
add_filter('pre_get_posts','mySearchFilter');