Optimal Settings.php for Pressflow + Varnish + memcache
Unless you are doing something quite unique, using boost &amp; varnish is usually overkill. If you have varnish setup exactly how you want it, I would just use varnish. 

Here is an example settings.php. It is a multisite safe memcache configuration thanks to the memcache_key_prefix setting.

&lt;?php
// Skip db query that checks for blocked IP's.
$conf['blocked_ips'] = array();

// Reverse proxy settings.
$conf['reverse_proxy'] = TRUE;
$conf['reverse_proxy_addresses'] = array(
  '127.0.0.1',    // Localhost
);

// Use memcache for caches, locks, and sessions.
$conf['cache_inc'] = './sites/all/modules/memcache/memcache.inc';
$conf['lock_inc'] = './sites/all/modules/memcache/memcache-lock.inc';
$conf['session_inc'] = './sites/all/modules/memcache/memcache-session.inc';

// Memcache Settings.
// Set memcache server.
$conf['memcache_servers'] = array(
  '127.0.0.1:11211' =&gt; 'default',
);
// Set memcache bins.
$conf['memcache_bins'] = array(
  'cache' =&gt; 'default',
  'cache_form' =&gt; 'database',
);
// Set memcache prefix to be the location of the settings.php file.
$conf['memcache_key_prefix'] = basename(realpath(conf_path()));
// Try to use a persistent connection.
$conf['memcache_persistent'] = TRUE;
?&gt;