One very interesting feature in confluence is admin delegation for spaces. And we use it a lot. But while a space admin may configure security/permissions based on users identity or group membership, he doesn't have the ability to modify any group. This leads to use alternatives such as:

• require the wiki main admin to add/remove user to/from groups each time
• do the thing with individual people instead of groups

I think local groups with space scope would be a nice improvement and would be really usefull.