After you successfully install memcached and pecl/memcached (memcached PHP support), you will next want take full advantage of it by enabling native support for memcached in magento.
NOTE: you must have memcached and pecl/memcached already installed. Otherwise your Magento installation will break if you try following this guide.
Ok... now that the warning is out the way. Here's how we do it...
Edit your local.xml