The mu-plugin developed to link major sites together for easy navigation has now been removed. Now that a common menu is being developed, navigation should be easier. The menu is still not complete but now that the login sits within the menu then the top bar is unnecessary repetition.
Cached files are still hanging around and so you might still see the header. Eventually those pages will be flushed.
[php]add_filter( ‘show_admin_bar’, ‘__return_false’ , 1000 );[/php]