When LinkedIn arrived, it seemed like a good idea -- sort of a way for people who aren't great at networking to see how to expand their network. Then, like any dating site, you needed to buy credits to participate, and only "players" are willing to do that. Then, they erased any additional value brought by their thought leaders by promoting third-rate content with catchy headlines like you mentioned. Now, why would I trust them with my resume? And if I have no interest in them, likely anything else on there is either out of date or some sort of lie.

Friendster, Myspace, Orkut, Facebook.... Similar things for social. Use the network to find more people to hang out with, feel less alone. But then, again, that is not actually a business and people aren't paying for it. So, you either show generic ads (not a bad idea) or you get people to pay to get their content in front of you. But then people stop caring about what they see there and move on.

I agree with other posters -- I used to keep Facebook around because my family was there. Now I don't even see their posts when I'm on it. So, there's no value anymore.