> Not to seem totally ignorant (I always open stupid questions with that phrase), but why does it matter if a third party knows your PSN? Is it used for something?

It *could* be used for anything. It's a serious invasion of privacy and infringement on your civil rights. With it turned on, it basically means that *ANY* remote system you visit could read your number. The data could be used to model your entire lifestyle, business transactions, everything. Our society already makes that too easy, but this is a giant leap in the wrong direction.