Currently, in Groups, anyone can just Pin to Group an activity item. That I think would create an issue when all of the members of the Group would just pin their post thinking that their post is important so it has to appear on top. Well, what if it happened? This is a half baked feature added to ES. It is a good idea though.
Wouldn't it be nice to have a setting in the backend maybe under Activity Stream to whether allow any members of clusters to pin an item or only the owner/admin.