When I joined LinkedIn, I did so because I wanted to keep in touch with people I worked with, like you know, a curated Facebook - which works well, because the people I worked with aren't necessarily interested in pictures of my baby boy or of me getting drunk this Holiday season and this goes both ways.
Unfortunately LinkedIn failed and failed hard at being that kind of social network. Nowadays the only thing I receive in return for my membership is Spam from incompetent recruiters that don't even bother reading my profile, and no matter what I do I can't turn those emails off (a perk you get for paying them), which is why I simply flag all LinkedIn emails as Spam.
I feel like LinkedIn missed a great opportunity here and now it's too late, their role being filled in my life by Twitter, GitHub, Google Groups and even Facebook.