The block_login_userinfo plugin has two views: As long as the user is logged out, it displays a login form just as block_login does. As soon as the user is logged in, block_login dispears. In contrast to this, block_login_userinfo displays pleasant information about the logged in user like his/her username, his/her avatar. Additionally, it displays a logout button where the user expects it to be: exactly at the position where the login button was previously.
Furthermore, for teachers and admins, block_login_userinfo shows exactly the same information as the login info section which is normally found in the top right corner of your moodle page - especially information about role changes and about failed user logins.
See README file for details