Recently i found a Post about Etags and thought this will be usefull for bandwith saving and faster response times in my scripts.

Just use this nice function:

function deliver_content($content)
{
	$etag = '"' . md5($content) . '"';
	if (!isset($_SERVER['HTTP_IF_NONE_MATCH'])) {
		$_SERVER['HTTP_IF_NONE_MATCH'] = '';
	}
	header('Cache-Control: must-revalidate, proxy-revalidate');
	header('ETag: ' . $etag);
	if ($_SERVER['HTTP_IF_NONE_MATCH'] == $etag) {
		header('HTTP/1.0 304 Not Modified');
	} else {
		echo $content;
	}
}

So all your content of this site will be cached in the browser cache, until the etag differs. I just used an md5 of the content, but you could use also other strings.