Overview
With the release of XenForo Release Candidate 1 (it will not work with prior versions of XF), nodes id are included in the templates, allowing us to easily change the Status Icons without any complicate template edits.
I know many of you already know how to do this by many others are...
You can run these queries on your database to mark all PMs as read:
UPDATE xf_conversation_recipient
SET last_read_date = UNIX_TIMESTAMP();
UPDATE xf_conversation_user
SET is_unread = 0;
UPDATE xf_user
SET conversations_unread = 0;