Nice addon, I installed it too, but I have one request:

Could you modify this so that there's a checkbox option to make the topic visible only to those debaters who have been specified? (and the mods and admins ofcourse).
I would like this, because it would prevent people feeling left out.

Really great mod and idea! Thanks for release.

I installed this but couldn't find userID ?? can I put username instead of UserID?

When regular user open a new thread, she/he don't know his/her userID to add in the private debate box.

I found the UserID in User profile. I am planning to make a list of UserID and post in my board. Is there any security issue if I display userID outsite my board? just wanna make sure....
For example:
User: timlennon (id: 27)

brilliant work!

I tried this on 3.6.4 and it didn't work. I logged out and could see a thread that was supposed to be between 2 registered users

Any way to allow this by group instead of member? Thanks.

I'm considering installing this... does anyone find it useful in flame wars or other 1-on-1 situations?

Anyone running this on 3.6.4 ?