There's a certain air of apathy permeating the crop of Thing 17 posts, and this has definitely affected how I've approached it. I can't remember anyone being enthusiastic enough about Linkedin that I thought it would be worthwhile to sign up for an account, and this post is therefore only a brief discussion of a few other Cam23 posts, and has no pretensions to in-depth analysis.
I read one of the further reading articles (the other has repeatedly returned a network timeout error), which made a fairly convincing case for being active on Linkedin if you're a business man, headhunter or entrepreneur. Now, while I'd love to be head-hunted for a top-notch special collections outreach post in one of the world's top libraries, I'd be surprised if they were looking for me on Linkedin. Unlike Andy Priestner, I just don't have enough enthusiasm to maintain my sticker collection just in case I'm wrong on this point.
The consensus seems to be that there aren't enough library types on Linkedin to make it a worthwhile networking resource. The Cam23 post says a much, as does Emma on her Thingymeblog. Magistra et mater has undertaken a small-scale experiment to compare take-up between Facebook, Linkedin and Academia.edu and concludes that "none of the sites really predominated, and none convinced me that I had to be on them. [...] Given how much it involves maintaining a presence on one of these sites, I think libraries are going to have to think quite hard about which services to sign up to."
It's not that I don't think that online networks are useful, but they're only any good if there are sufficient active people with a similar interest. One up-and-coming network to watch (or join) might be the LIS New Professionals Network. With about 230 members at the time of typing, it has a resources area, jobs RSS feed, and forums for discussions of LIS courses, chartership, and all manner of other things. It's only been recently launched, and there's a certain buzz about it at the moment. Hopefully this will continue in the coming months, as this seems like a much better way of keeping in touch with colleagues.