Personally I don't think making the forum private is a good idea at all. I really don't think it is needed and I feel it kind of goes against what is trying to be accomplished.
We want to try and get as many people into the forum as possible, one so that we can justify having our own sub forum and two so that people can read great stories and learn how to give proper feed back. I dont see any problems with having people lurk in the forum, you never know how it will inspire someone.