As mentioned in a recent tweet of his, Andrei Zmievsky has release the latest version of the memcached extension with an interesting new feature:

Just released PHP memcached extension v0.2.0, now with JSON serialization support: http://pecl.php.net/package/memcached/

This extension can be adding into your PHP installation to allow direct interaction with memcached servers via the libmemcached libraries and the server's API. You can grab the most recent version of the extension from this github page.