I have used LinkedIn for a number of years. I like that it gives me a public profile that I control, and in fact I don’t actually keep a paper CV any more, but I do update LinkedIn when something changes in my job or I gain a qualification. This ‘thing’ has inspired me to go and tweak it further!
It is useful for connecting with people you meet through work, its a way of keeping loosely in touch without the over sharing or context collapse of FaceBook!
The student case study for LinkedIn was interesting, I’ve not been approached for a post via LinkedIn, but it is certainly nice to think that it might happen!