In the 90s it was said that almost anyone carrying a briefcase in New York was a headhunter. Easy entry barrier, as long as you were connected. Now, thanks to LinkedIn, things have changed.

At first, LinkedIn depended on recruiters, who used its premium services to find out about potential candidates, and in 2009, 40% of its revenues came from these premium services. Now, according to Michael Overell at ere.net, LinkedIn has become a category killer that has marginalized a recruiter’s greatest asset: access to talent. As LinkedIn put it last year, “We believe our solutions are both more cost-effective and more efficient than traditional recruiting approaches, such as hiring third-party search firms, to identify and screen candidates.”

We can’t say whether or not this was always part of LinkedIn’s grand design, but we do know this: an awful lot of the action on LinkedIn appears to be coming from people in the market for that next assignment – and advertisers looking to attract their attention. Yet another example of a sector being transformed by a dominant early mover, and real-live professionals being disintermediated.