Currently it synchronizes the username, password, and e-mail address. When changes are made in Joomla/CB then they get updated in phpbb... phpbb changes are NOT transferred back to Joomla/CB since I currently have no MODS or HOOKS for the phpbb system implemented.
As far as PM systems... I have some CB Connector modules that allow you to view the phpbb PMs in Joomla/CB... but there is no syncing of PMs or anything setup to help with multiple PM systems...
Greg