Right now in the private message area, the "Delete" and "Delete All" buttons look very much the same and it might be easy for someone to select a couple of messages then click delete all and find that ALL of their messages are suddenly gone instead of the two intended ones. Not that I would be dumb enough to do such a thing myself, but someone less observant could. Since there's no trash can something like that could be really permanent.
I don't think the button is really necessary since it's easy enough to "Mark All" then "Delete".
