[nerbert]

That would be a very difficult feature -- the adminCP setting would be $vbulletin->options['f_default'] but to work it would have to place the forumid string into $vbulletin->userinfo['f_ignore'], which would require an update query for all users every time you change it. In fact it would be difficult to write code that wouldn't do that every time you change any setting.

I doubt many people would get any use out of such a setting anyway.