Local cache for gravatar images (saves dnsqueries and let you control cache/proxysettings of the images).
This can happen, if there are many gravatar images that need to be updated... Shoudn't be a problem since version 0.9.2.
GravatarLocalCache depends on the use of get_avatar() (a WordPress function). If your plugin/theme doesn't use this function, GLC can't fetch the gravatar requests. Ask the author of the plugin/theme to use "get_avatar()".
For any further questions, please use the support forum.