I see that there are currently an unlimited number of potential invitees to private topics? I would like to see an option to limit this to an arbitrary number, otherwise we are essentially granting users the ability to run private forums on our sites.

This might not be a problem for everyone, but I want to be able to control the content on my website, and exclude discussions of a pornographic or illegal nature. Private, user-run, unmoderated forums take away my ability to control the content of my site. I'd like to be able to limit the number of participants in a private topic to perhaps 3 or 4 at a time, to eliminate my liability at perhaps finding out too late that a large private forum of child-pornographers, drug-smugglers, or terrorists are using my site as a gathering place using private topics as a way to conducts business with no prying eyes.

So! Am I the only one worried about this aspect?