When implementing conferencing I've noticed that <privacy/> does not seem to work. I send it in the IQ after the initial presence is sent to the conference:
If you create the conference by sending presence to it, you get the old-style groupchat protocol, which I believe doesn't support privacy. To get privacy you need to create the room the new way. The conferencing draft document describes all this.
http://docs.jabber.org/draft-proto/html/conferencing.html
(Look under "creating a new room".)
Watch out though, the current draft of this document describes all kinds of new features that I don't think have even been implemented yet! As far as I know there's no current document that describes just what exists today in 1.4.x.
�Jens
