Worked out a server-side caching mechanism for PHP based sites. This is extremely helpful to performance. Somewhat like the concept of a reverse-cache sitting in front of a webserver, like squid, but this can be used on those hosts that don't have that software installed. Here is a snapshot of the PHP code, usage should be self-explanatory. I just started testing it, but so far so good.

function pageCacheStart($ttl=600, $debug=FALSE, 
  $cacheDir='/tmp/pagecache', $sidName='psid') {
  global $HTTP_SERVER_VARS, $HTTP_GET_VARS,
$HTTP_COOKIE_VARS;

   //to force the cache OFF, uncomment next line
  //return FALSE;

   // we only use the cache for GET requests.
  // we don't use the cache for ssl requests.
  if ($HTTP_SERVER_VARS['REQUEST_METHOD']!='GET'
  ||  isset($HTTP_SERVER_VARS['HTTPS']) ) {
    return FALSE;
  }

   $REQUEST_URI = $HTTP_SERVER_VARS['REQUEST_URI'];

   // if we have the sid in the get vars,
  // and we have the sid in the cookie vars,
  // then we can act as if the sid is not in the get
  // vars and return a cached page.
  // if the sid is in the get, and not as a cookie,
  // then we don't use a cached version since all the URLs
  // in the page need to be rewritten with the sid by php.
  if (isset($HTTP_GET_VARS[$sidName])) {
    if (isset($HTTP_COOKIE_VARS[$sidName])) {
      if (count($HTTP_GET_VARS)==1) {
        $REQUEST_URI = $HTTP_SERVER_VARS['SCRIPT_NAME'];
      } else {
        $REQUEST_URI =
ereg_replace('&'.$sidName.'=.{32}','',$REQUEST_URI);
      }
    } else {
      return FALSE;
    }
  }

   // get the hostname
  if (isset($HTTP_SERVER_VARS['HTTP_HOST'])) {
    $HOST = $HTTP_SERVER_VARS['HTTP_HOST'];
  } else {
    $HOST = $HTTP_SERVER_VARS['SERVER_NAME'];
  }

   // cache directory use for pages from this host.
  $cacheDirHost = $cacheDir.'/'.strtolower($HOST);

   // build the name of the cache file for this page
  $cacheFile = $cacheDirHost.'/'.md5($REQUEST_URI).'.cache';

   $mtime = filemtime($cacheFile);
  $time  = time();

   if ($mtime >= ($time - $ttl)) {

     //send cache control headers that let client browser
    //cache the page.
    header('Expires: '.gmdate('D, d M Y H:i:s', $time +
$ttl).' GMT');
    header('Last-Modified: '.gmdate('D, d M Y H:i:s',
$mtime).' GMT');
    header('Cache-Control: public');
    header('Cache-Control: max-age='.$ttl);

     //get the cached file and send it to the browser
immediately
    readfile($cacheFile); 

     //debug info
    if ($debug) {
      print("<hr>CACHED COPY
filename: $cacheFile\n");
      print("
mtime: ".date('m/d/y h:i:s
a',filemtime($cacheFile))."\n");
      print("
cache age
".(time()-filemtime($cacheFile))." seconds\n");
    }

     //exit this server session
    exit(); 

   } else {
    // the directory existence is the signal that pages
    // from this host should be cached.
    if (!is_dir($cacheDirHost)) {
      return FALSE;
    }

     ob_start();
    print("<!-- request: ".$HOST.$REQUEST_URI." -->\n");
    return $cacheFile;
  }
}

 function pageCacheEnd($cacheFile='', $debug=FALSE) {
  $html = ob_get_contents(); 
  ob_end_flush(); 

   if (empty($cacheFile)) {
  } else {
    if ($debug) {
      print("<hr>writing new cacheFile: $cacheFile\n");
    }

     if ($fp = @fopen ($cacheFile, 'w')) {
      @fwrite ($fp, $html);
      @fclose ($fp);
    }
  }
}