Create a simple interface to add/remove a single user to/from multiple groups at once. When you identify/select a user, it will show you two select lists. The right side will list all of the groups the current user is a member of while the left box shows all the groups the user is NOT a member of. Between the two select lists are buttons to ‘move’ the groups from one side to the other for the identified user (while modifying their memberships appropriately in the process). The select boxes are configured to allow multiple select so you can usually perform the maintenance in just a couple clicks.