Topic: Damn! You've converted me.
When I first discovered PunBB I was very impressed but disappointed to see a lack of built in PM system.
I've since installed PunBB on my main site (and 1 other) and I can honestly say that despite having thousands of active users, we haven't missed having a PM system at all. Everyone just sends form mail, which is actually more efficient.
I bow to your superior judgement Rickard (but I won't be eating my hat!).