In EE 2.8 and above, you can select 'Memcached' as your 'Caching Driver' under "Admin" => "General Configuration".
I am using one of Nexcess' "ExpressionEngine optimized" hosting plans, which lists "Memcached Back-End" as one of their features. I wanted to enable this, so I contacted their support folks. They set up a socket to use memcache.
However, when I select 'Memcached' as my caching driver, EE displays the error message "Cannot connect to Memcached, using File driver instead".
What is the correct syntax for my config file to get this to work?