Mike Carper (aka mikeytown2) talks about the Boost module, which a lightweight performance enhancement for small-scale sites that don't have a lot of dynamic content. After adding some apache rules to the .htaccess file, then Boost will translate Drupal pages into static HTML files and serve those directly instead of going through PHP and MySQL. Carper talks about some of the other caching configuration options, and says that this module is perfect for sites on shared hosting that are looking for a performance boost. He says that Boost can actually make your site slower in some cases where you have a lot of content that is frequently updated. In those cases, Varnish would probably be a better solution, but the Boost module is intended to be a quick and easy solution for smaller websites looking for better performance.