Re: Hey Andy, this time about forums
Another alternative instead of separating WPMU & bbpress capabilities: you can assign specific user meta for each users. Say, the meta value is an array containing all forum ID that specific user belongs to. Of course you need to write some hack to the bbPress side as well. That way you can share both public & private forums in a single bbpress install.
Just an idea. I haven’t look into the code too 
