Anyone see it yet? It lets you add any and all your friends to groups you're a part of. Go to a group page you're part of, on the right there'll be a link saying "Add friends to group...", select friends, and presto! All those friends are now members of the group. Next you go to your group admin, and send out a new mass email to your newly updated userbase, and suddenly you have a bunch more subscribers to your email spam newsletter. Best part? It doesn't look like you can disable it.
I just created a group to see if group admins could do that and still no. The only similar option I get is "Invite people to join".
Well, tbh there was nothing stopping you spamming all of your friends with messages to begin with. If it allowed you to add people to the group who weren't your friends then there'd be a problem.