Is there a way to unpublish events automatically after their date?

I have solved the problem by writing the following ultra-simple module called eventhide. If an event is more than a day old, then it's 'changed' date is set to 1999-12-31. I have replaced the standard taxonomy view using the views module to exclude nodes that have changed dates before 2000-01-01 and to put the items in ascending order. Stickies will still show at the top. The advantage of this approach is that if an event gets modified so that it is in the future again (e.g. by recycling old events), then the 'changed' date will automatically be updated and the event will be unhidden.
The code shows an alternative line of code which will unpublish events, but then of course they will disappear from the calendar.

I would value any comments on the code:

// $Id: eventhide.module,v 1.0.0.0 2006/08/06 17:30:14 Andrewfn Exp $

/* If an event is more than a day old, then it's 'changed' date is set to 1999-12-31.
 * To use this, replaced the standard taxonomy view using the views module to exclude nodes that have changed dates before 2000-01-01
 * and to put the items in ascending order. Stickies should still show at the top.
 * The advantage of this approach is that if an event gets modified so that it is in the future again (e.g. by recycling old events),
 * then the 'changed' date will automatically be updated and the event will be unhidden.
 * The code shows an alternative line of code which will unpublish events, but then of course they will disappear from the calendar.
 */

/**
 * Implementation of hook_help().
 */
function eventhide_help($section) {
  if ($section == 'admin/modules#description') {
    return t('A module to hide events that are out of date by setting [changed] to before 2000 so they can be filtered out by the views module.');
  }
}


/**
 * Implementation of hook_perm().
 */
function eventhide_perm() {
  return array('mark event nodes that are out of date');
}

/**
 * Implementation of hook_cron().
 */
function eventhide_cron() {
  $clear_cache = FALSE;

  //if the event_end time is more than a day old, set the change date to 1999-12-31 so that the query module can hide it
  $nodes = db_query('SELECT * FROM {node} n LEFT JOIN {event} e ON e.nid = n.nid WHERE event_end < %d -86400 AND changed > 946600000', time());
  //alternative line of code to unpublish the node (to use, comment previous line and uncomment following line)
  //$nodes = db_query('SELECT * FROM {node} n LEFT JOIN {event} e ON e.nid = n.nid WHERE event_end < %d -86400 AND n.status = 1', time());
  
  while ($node = db_fetch_object($nodes)) {
    //if this node is to be hidden, we can update the node
    db_query('UPDATE {node} SET changed=946600000, promote=0 WHERE nid = %d', $node->nid);
    //alternative line of code to unpublish the node (to use, comment previous line and uncomment following line)
    //db_query('UPDATE {node} SET status=0 WHERE nid = %d', $node->nid);
    
    watchdog('content', t('%type: scheduled hiding of %title.', array('%type' => theme('placeholder', t($node->type)), '%title' => theme('placeholder', $node->title))), WATCHDOG_NOTICE, l(t('view'), 'node/'. $node->nid));
    $clear_cache = TRUE;
  }
  
  if ($clear_cache) {
    // clear the cache so an anonymous poster can see the node being published or unpublished
    cache_clear_all();
  }
}