Varnish is front-end web proxy that I've been using with my Drupal sites for 18 months now. I talked about it in a presentation at Drupal camp with Khalid . A front-end web proxy means that instead of visitors directly accessing the Drupal site, they go through a caching layer. I like to think of varnish as a protective bubble around Drupal. Using Varnish has a number of benefits, and in my presentation I was particularly interested in demonstrating how it enables a site to survive huge spikes of sudden traffic , beyond what a web server would normally be able to handle. So that's one of the benefits. Another important benefit is to reduce the load on the server , enabling better response. Or more cynically, it would enable you to pile more sites onto your server. But to explore this more closely: by moving most of your 'easy' page loads out of the php/apache stack, you can tune your stack better to what it's got to do - and you're not wasting 128Mb or mo...