As currently stands, creating new groups and adding more than five members is a significant administrative overhead.

The ability to add users in bulk via the Group itself would be considerably more efficient, and more in line with common system administrative practices.

Example: Our board encourages users to gather together in smaller groups to organise teams to work on specific projects. At present those users must then ask an Administrator to not only create their team's subforums, but then also to add upwards of twenty users to the group which has access to those subforums. Manually editing all 20+ users to add them to the new secondary group takes significantly longer than being able to add them by username from the group itself (e.g. using the Conversation username lookup functionality to add multiple users) would take.

Likewise, removing members as group membership fluctuates should be as simple as going into the group's membership list and clicking a little X by their name to remove them, much as you would remove users from a conversation if you had accidentally added the wrong one.

You may want to check out Groups Collaboration on the Marketplace by @Kevin Carwile