I have been using Facebook for a couple of years and I am quite attached to it as a way of (a) keeping up to date with friends and (b) reconnecting with friends I haven't seen for a while. It has been particularly useful as my family and I moved from Kent to Berkshire about 3 years ago (how time flies). However, despite being a fan of Facebook, it is something I keep very definitely in the realm of the personal, rather than anything work related. I do have colleagues I am friends with, but our interaction is informal and rarely mentions work.
I haven't tried LinkedIn at all (although I will admit to having a nose around when my husband logged in). I can definitely see the benefit of it, in his industry (HR) where contacts are everything - he has even found contracts which were only advertised through LinkedIn. However, if I'm honest, I have felt that it wasn't really relevant to school librarians, who tend to work in relatively small networks. But the guidance for this 'thing' has made me take stock and reconsider this notion. In my thirteen years as an information professional, I have already worked in three sectors (commercial law, public libraries, schools) and where else can I bring together the contacts I have made across all three? Having seen the suggested examples, I think it is time to have a go - a project for the summer holiday maybe?
As for the other suggested online networks, I have engaged with a few via Twitter, but others I need to investigate further. Pininterest, for example, I hadn't really twigged what it was, but when I looked at the site I realised I have seen it used to group images together like an electronic mood board. Again something I might try out over the summer - maybe as online extension of our displays.
Overall, I am a fan of online networking. I think it opens us up to so many more opportunities than we could hope to be part of without them; and I think Reid Hoffman's "Facebook is the backyard BBQ; LinkedIn is the office" quote is a brilliant way explain the differnce between the range of sites available.