I've just joined another Drupal forum, and I think that they have a module that might be of benefit to people here. It's called "Forum select" and it allows each user to show or hide each forum. Not sure if it takes them out of the tracker ("Recent posts"), I'll have to get back to ya on that one. I would think so, though.
For example, I never use Thunderbird, and that would be one topic I'd hide.