LinkedIn has over 290 million professional users and growing. The membership is a very focused metric which most career oriented types need. Getting a well paying job.
As they open their platform to new applications manufacturers; revenues will grow and new products will be introduced.
Facebook has had more publicity but LinkedIn has better metrics on their users. Facebook whatever and I like cupcakes. LinkedIn identifies salary ranges, education, propensities and other actionable digital intelligence.
George Gutowski writes from a caveat emptor perspective.