In the specific context of when you're following someone; and in general, what is it? What am I connect to and what's an open stream.
I do understand if you check "inbox", then the followed person's activity will show up in your inbox.
You can essentially set up a specific forum sub categories to funnel into the stream. So rather then actually navigating the forum, you can be provided real time updates in you're specific stream.
For instance: I have all of the Activision support forums being directed to my "Support" connection stream I created.
Hope this helps,