There are currently hooks when a user or site is deleted, but not when either are added or updated.
use cases: - addUser/updateUser - 3rd-party plugins that want to sync with their own user database and provide their own authentication mechanism - addSite/updateSite - see BotTracker in #2391
(In ) fixes #2580
Updated http://piwik.org/docs/plugins/hooks/ - SitesManager.addSite, SitesManager.updateSite, SitesManager.deleteSite - UsersManager.addUser, UsersManager.updateUser, UsersManager.deleteUser
Nice one :)