As well known from the good ol' IRC-chats, it is possible with XMPP-groupchats
to open private conversations with people in the chatroom.
Jitsi has two issues with this:
1) Jitsi does not support to start a private conversation, as the user is not
presented with an apropiate option in the roomlist or the menu.
2) If another client starts a private conversation the message arrives
normally but when the user tries to answer Jitsi fails to send the messages
with an delivery-error-message. As even in a non-anonymous groupchat the room-
JID is displayed instead of the real sender-JID this seems to be an issue with
the determination of the correct sender-adress.
So overall this feature is effectivly unusable till Jitsi nightly 2.3.4756.