A while ago I had a recruiter try to, ahem, coach me on my CV, which apparently had too few details (apparently still enough to have this interview, but the irony was lost on her) and on my LinkedIn profile, which wasn't up to date and also had few details (deliberately BTW, as I was getting spam).

My gut feeling is that while there certainly are people who benefited from using LinkedIn, but for the majority it's just a vessel for being terminally online and a waste of time.