For me Linkedins’ value can be even much more than 1 billion. Where they lack is a strong marketing campaign where Premium Membership is transformed into a status symbol. Also the heavy users (500+ people) should be granted free access to some kind of a status and free extra services (with their earned status). There should be a schema similar to Credit Card business.
I am sure Linkedin has plans in these areas. I think these things are really hard to implement but doable in right hands. Hopefully, they will reach the right talent to make Linkedin the major player on online networks.