As with other commentators, I strongly suggest that this article should at least be ignored, but better would be for the author to remove or rewrite it. For better information, search for Mark Nottingham's caching tutorial.

There is no benefit to removing Last-Modified. As Klaubert rightly points out, doing so will eliminate the chance of a 304 on revalidation, forcing the server to resend the full payload.

Last-Modified should always be used in conjunction with Expires. For objects that do can not support a Last Modified header, e.g. dynamic .php, .jsonp requests, use Etags.

Removing the Last-Modified header seems totally useless. I tested on Firefox with "FireBug > Net" (Firefox versions 3.6 and 11.0)

If you close the browsers and re-open it, and then you navigate to the page you previously viewed, you will see browser hitting the server with an HTTP request for each resource (images, etc.).

After the HTTP request, the server replies with 200 OK and the browser decides to take the image from cache instead of downloading it from server, but the browser has still inquired the server for each image with an HTTP request, so it's NOT true when in this article they say: "...this is a really unique trick I promise) eliminate any validation requests!!"

FYI: this issue was discussed also on stackoverflow: because the same problem arises even when using Cache-Control: max-age=31536000 header.

While this is an old post, it is still very useful. I have a question if you dont mind:

Is there a way to Combine external JavaScript using htaccess?

If there is how is it done?

new browsere ( ie8 , firefox, chrome) ask again the resource if they do not know when was last modified!

so this article should be changed since make damages

Thanks

Removing the ETag header is ok (each server generate a different ETag, in a cluster/farm this will be a problem, not a solution). But by removing the last-modified header you will make the browser use the "Expires" only, when the content Expires on browser cache it (the browser) will fetch a new content, regardless if is modified or not. If you use Expires and last-modified together, the browser (firefox on my test, YMMV) use the Expires, and after that it start to use last-modified getting the 304 (not modified) as a benefit. This way you get a two layer of cache: 1- absolutely local, 2- Browser e Server if-modified-since/not-modified handshake;

Klaubert

ErrorDocument 401 http://www.site.co.uk/401-page.html
ErrorDocument 404 http://www.site.co.uk/404-page.html
ErrorDocument 500 http://www.site.co.uk/500-page.html
 
RewriteEngine On
RewriteCond %{HTTP_HOST} ^site.co.uk [nc]
RewriteRule (.*) http://www.site.co.uk/$1 [R=301,L]
 
ExpiresActive On
ExpiresByType image/ico A29030400
ExpiresByType image/gif A2592000
ExpiresByType image/png A2592000
ExpiresByType image/jpg A2592000
ExpiresByType image/jpeg A2592000
ExpiresByType text/javascript A2592000
ExpiresByType text/css A2592000
ExpiresByType text/swf A29030400
ExpiresByType text/js A29030400
 
Header add X-Enabled mod_gzip
Header add X-Enabled mod_deflate
Header set Cache-Control "private"
Header set Expires "Thu, 27 Jul 2011 10:00:00 GMT"
 
FileETag none
 
Header unset Last-Modified

Is the file correct - are there clashes/ etc. Current pagespeed score is 91% and yslow gives it a Grade A. Before I move on to learning about CDN's, I need to make sure I'm on the right track with htaccess files!