We're testing the new version of Joomla support for Varnish HTTP accelerator. Version 1.2 is available for Joomla! 1.5 and 2.5. Take a look at the changelog.
Don't cache a page with error box - when JError::raise() is called or JDocumentRendererMessage is used, a header which forbids caching is being sent
Prevent displaying cached pages directly after logging in.
After successful login the user is usually redirected to referring page. In many cases the page is cached by browser, and contains a login form, thus causing confusion to the user. The problem is solved by adding a random GET variable called _rnd.