Memcache integration is not loaded
You've got to add these lines to your settings.php file to run memcache proper:

$conf['cache_backends'][] = 'sites/all/modules/memcache/memcache.inc';
$conf['cache_default_class'] = 'MemCacheDrupal';
$conf['cache_class_cache_form'] = 'DrupalDatabaseCache';


If you're on top of a multisite installation also don't forget to add this one: 

$conf['memcache_key_prefix'] = 'unique_key';


More information about configuration and setting memcache for drupal you can find here.