Sarah's instructions wisely gauge the likelihood of account fatigue at this stage of the game. But I can report having looked at the prescribed LinkedIn profiles, and also at Phil Bradley's, what I could see of it without an account of my own, and at the two that wife Clare has got up at various times. Only two; one of those in the screenshot is for another lady altogether.
Clare's experience of LinkedIn is that of one pursuing a portfolio career in science. She holds down two part-time lectureships and engages in much science journalism. She has noticed this difference between the Twitter and LinkedIn communities, that the scientists (mainly biotechnologists) tend to favour LinkedIn while the journalists tend to favour Twitter.
I don't know if there's any significance in that. But it is probably symptomatic of the fact that LinkedIn fits some communities better than others. Andy's (of all people's) lack of enthusiasm for this business resource has much to do with the fact that "LinkedIn isn’t really being pitched at someone like me". I have a similar sense of it, and, with my account fatigue, I don't see a compelling reason for joining. Not just yet, anyway.