I agree with most of the above wish list and would like to add:

1. A control panel method for pruning private messages, preferably by date and/or user and date. My database has PMs stored going back years.

2. A way to suspend a post after it's been posted. I don't moderate all the posts on my forum but once in awhile someone posts something I want to suspend while I talk to them. Right now, my only option is to delete it or leave it up.

#18 above - I created a user group that doesn't allow PMs and I put PM abusers in that group. What would be better, IMO, would be to allow admin to suspend a user's PM privileges on a case-by-case basis, in the member management section of the control panel.