[peteretep]

Coming at it from a slightly different angle (this is my sector)...

The big problem with LinkedIn is that it's a Jobseeker Database masquerading as a social network. They make their money by selling you to recruiters. That's the central cause of almost all the behaviour people don't like. The second part of that is that the social network part - the stickiness angle - really isn't a natural part, which is why it's so irritating that it wants to notify you that someone you worked with once published an article.

I'm afraid I don't know the killer features or the solution, but that's the root issue.