Even if I'm not following someone, I can easily see what they're doing via advanced search.
You don't even have to do a forum search--I found that if you click on someone's avatar and then go to their 'messages' (actually you have to click on the number of messages), you'll see the list of that person's forum posts. Works just like our old 'see forum posts' feature, only posts are now called messages. And messages (private) are called conversations.