LinkedIn works if you just treat it like an online CV; Keep your details and work history up to date, and ignore all the other social crap. My last two positions came from recruiters finding me via LinkedIn, so for some disciplines it still has merit.

I don't use it because I'm coming to the end of my working life, I don't expect to interview again. However if I was earlier on in my career I would be managing my Linkedin profile quite carefully.

I just got the best gig of my life through LinkedIn. But I was abroad so not really able to physically network as such.

using the kill newsfeed extension for Linkedin makes the app bearable for me.