[@robin-w Moderator 12 years, 3 months ago]

bbpress has its own roles

so user not registered would see all public forums but not able to post, but would not see private forums
registered users with wordpress roles would be able to do all wordpress things but with ‘no role’ in the user profile under forum would not be able to post in the forum.
registered users with forum roles (eg participant, moderator) would be able to see public and private forums, and if wordpress roles set would be able to carry out wordpress roles
registered users with spectator role would be able to view both public & private forums but not participate.

you should be able to achieve whatever you want with a role based solution.

come back with further details if this is not what you are trying to achieve