[kylake]

PM is definitely a nice feature if used for the right reasons. If you want to pass information like a phone number you would not want in the public domain.
As booger said the, admin of the board, can most certainly see everything about the board and that is the way all board architecture is. Admin has complete control.

I was on an Isla board operated by a Bob C. that was a great board and just like this one with an open policy about what could be posted. A few users for some reason started plotting against Bob and a few users on the board using PM. Boy, was that ever STUPID.
Bob didn't make any big deal of it but since he could read what they were plotting he would turn the tables on them time after time. It was truly funny to watch/read.
They finally, we permanently purged after being to big of a nuisance.