I like this idea since you can make some boards invisible to everyone but a choice few. The problems I see are that it would be hard to figure out who's good enough to be let in and are the ones who are good enough in need of answers to questions.I don't know if this is possible, but with phpBB you can define usergroups. Why don't you (I mean mods or webmaster) make an advanced usergroup and add the mods and some expert members part of that group. this group will be the only one that is able to post on that board and the mods will have to move interesting threads to that board.
But keep the group select. handpick the members on their qualities. (I can only think of four members who are not mods that I would put in that group)
How about instead of just an expert board, it could also be a design board, and expert discussion. That way the true experts have a release and those not quite expert but who have an idea of what's going on can still ask advanced questions.
From what I've seen, there are a bunch of members who never ask questions and apparently don't need to, Salem, Sayeh, Quzah, Hammer, Prelude, SilentStrike, Fordy, and Adrianxw come to mind. I can't see an expert board helping them unless it goes past questions and answers.
On the other hand there are a bunch of members who know enough to do the simple stuff, but still have more difficult problems, they're ideal for this new board since they still have questions, and they also can participate in expert discussions.
Things like syntax can be considered beginner, but algorithms and data structures and stuff like that would work better in a more advanced board. To keep the newbies out all you have to do is figure out who's good enough and let them see it. If someone answers a good question but isn't allowed into the board maybe the thread can be moved and the poster allowed to see just that thread.
That's my 2 cents, ignore me if it's stupid.
