Hi, Moodle (moodle.org) has a feature like this but it is extended a little more: the admin has to possibility to logout from an user. Take a look at the following picture: http://www.unitbv.ro/cat...
The 'Switch to user' dropdownlist is unsorted or not sorted by username. When you've got a lot of users in your portal it's (almost) impossible to find the user you need.