In reply to sebastien:
The funny thing about Linkedin is that everyone appears to be remarkably successful....
I'm not a recruiter but I do look after recruitment for the firm I work for and if someone we were interested in wasn't on Linkedin, I wouldn't see this as a bad thing. Rather just a personal choice of that individual not to be on Linkedin.
I'm on there as I work in a very niche area of tax and there's not many of us about, hence why it's quite useful to make recruiters aware of my existence!