I worked further on a Plone add-on to manage conferences and had to work with the navigation root of a Plone site. I moved this navigation root to the container object of the conference add-on. The navigation worked as expected yet (the objects in top container made it to the main navigation menubar), but the login and register links at the top of the site didn’t work anymore. Thus I had to edit the links of this actions / portal_actions inside the ‘Site Setup’ or the Plone ‘Management Interface’. I added a short howto about this.