I agree with you but I wouldn't be so stark. My email address book is still the one thing that I maintain and keep up to date. As social networks come and go, that address book remains current. That's why a lot of social networks will offer to import my contacts when I sign up to a new service. Email is the reference and is constantly being leveraged.

Also, as the article says, the initial impetus of connecting with friends of friends and old acquaintances from high school quickly wears off. Once that fun is gone, what is left is a broken and boring network that might not be so valuable to a business.