-- Communities can now have custom security groups created for them. Only community owners and maintainers can create or post to custom security groups for the community. A new security level of 'maintainers' has also been created, which can be used by the community owner/maintainers to post entries that will only be visible to the current owner/maintainers of the community.
-- Community owners & maintainers can now opt to receive pingback notifications when their community is mentioned by others on LiveJournal.
-- Notifications are now sent correctly for replies to anonymous comments.
-- Incorrect profile page friend & membership counts are fixed.
-- Links to ICQ accounts in the External Services section of the profile no longer link to an invalid URL.
-- If a user you have banned uses your username in an entry or comment, it will no longer generate a pingback notification.
Please see this post in lj_releases for full information and links to the pages where community maintainers can set up these new features.