Isn't pming like backstabbing gossip?
a pm is just a message format.. most who I have contact with via pm I also have their e-mail and phone...
as with any message or conversation.. it depends on the context... if your discussing another person.. then yes it could be gossip... it could be backstabbing..
or it could just be a polite thank you for their support or to clarify a persons comments..
or it could be downright harassing ...