Currently to add 100 uses to the same group (after they are created) I need to edit each user and modify the groups they are a member of. A nice enhancement would be to provide this same interface (editing a users associated groups) to the group browser where an administrator could bulk select which users should be associated with which groups.

The admin would click on a group in the group browser and see a list of all users not in that group and a separate list of all users in the group, and then get to move users between the lists just like editing a user's groups works now.