That title is misleading. Facebook isn't selling access to anyone's Inbox. They are selling the ability to purchase the right to send messages to non-friends. Using the strict filter setting, the messages (like PMs) go to an "Other" folder rather than as they would in a private conversation with a friend. Apparently, the Other folder has been there all along.
Yes, the first thing is to use an alternate e-mail address. Unless you're a well known person who is using FB to publicize their work (i.e., Mark Russinovich), make your posts visible to friends only or even a custom list. Just like with Google and Hotmail, I refuse to list my cell phone as an alternate method of getting a password reset.
Of course, Facebook is about money. They aren't going to donate all that server space. When family members are spread across the U.S. & Canada, Facebook is a convenient way to share news and pictures.
A Guy, do you mean e-mail notices? I have my settings so I don't receive any e-mails.