I suggest "Shout Box per Forum" feature.
Each forum is attached a "Shout Box". (or an option , that some forum can have their shout boxes , and other forums share the global shout box)
Some users are familiar with each other only in some forum. They are "friends" in one forum , but when they enter another forum , they feel un-comfortable , unfamiliar.
If each board is attached a shout box (of course , it must take forum authorization into consideration), they can stay in their forum and discuss forum-specific issues online.
Currently , the Shout Box is global , it can be preserved , used for portal pages , or forums without specific shout box.
