Was playing around with APC and memcache(d) and installed them. I did not add an extension=memcache(d) to /etc/php.ini though. However, they still show up in phpinfo as the .so modules are in /usr/lib/php/modules. I am assuming that is normal?
At present, I enabled 'File' caching as the back end in library/config.php, but thinking of going the memcache route. Not sure if I need it though. Currently on a GD VPS.