The value I see in LinkedIn:

1. My linkedin contact list is >300 people that I worked closely with over the years and all have seen me kick ass. I have actual email addresses for <10% of them.

2. I can browse my list and see where they are currently working. "oh gee, Mary works at coolCo, I should reach out to her because I' like to work for/with coolCo."

3. When I want to let them know that I started a new business venture, I can send them a message that is less obtrusive than an email.

4. If I give a prospective client my linkedin, they can see a) a brief summary of my resume, b) that I have a lot of contacts in x space, and c) that they may know some of the people I have worked with over the years. These all give me some measure of credibility.

Both my current job and my previous job were initiated by recruiters who contacted me on LinkedIn.

LinkedIn has been extremely valuable to me. The recruiters who contact me are usually from professional executive search firms and highly relevant, though I only get a few a year.

I think the level of relevance depends on the industry though. I'm in finance/banking and fairly senior.

I think people's job patterns varying is part of it. For me, I've mostly stayed at my relatively few jobs for a long time (10 years or more) and every job after the one immediately after grad school have been through people I knew. Others are hopping around a lot more and are more often through recruiters looking for some particular keyword skill.

LinkedIn is pretty useless for the former--except as a Rolodex--but anecdotally can be very useful for the latter.