// ****** DATASTORE CACHE CONFIGURATION *****
// Here you can configure different methods for caching datastore items.
// vB_Datastore_Filecache - for using a cache file
// $config['Datastore']['class'] = 'vB_Datastore_Filecache';
// vB_Datastore_Memcached - for using a Memcache server
// It is also necessary to specify the hostname or IP address and the port the server is listening on
// $config['Datastore']['class'] = 'vB_Datastore_Memcached';
// $config['Misc']['memcacheserver'] = '127.0.0.1';
// $config['Misc']['memcacheport'] = '11211';

These are the default 3.5.4 settings for the datastore cache configuration.

Do you use these, and if so how and why? Do you notice a difference?

I don't know what they do, and as such are loathed to change them. But if someone who knows what they are doing would advise their use and explain how to use them I would be happy to. :)

We use the filecache on WT and it makes a noticeable difference, or at least it did when our server was at a crawl (before we upgraded our dedi server).

yeah, I use the filecache, huge difference even on my smaller site.. memory cache, never tried it