In the initial user group, people have to have all their posts moderated. Once a post has been approved, they can post without moderation and have access to the rest of the forum.
For some reason, the promotion to the normal member usergroup (the one that they get promoted to after 1 post) doesn't seem to be working - the last few registrations I've had to manually promote.
There aren't any error's anywhere, it's just this promotion doesn't seem to be working.
It looks like other promotions are working, but I can't be sure on that one.