Lawyers hit an easy target
1. I don't know anyone who has knowingly given LinkedIn permission to go over his/her contacts - that would be necessary to prompt the user to send an invite.
2. I definitely received invitations and reminders to email addresses that could not possibly be in the contact lists of the people who invited me. And I asked them to check - they weren't.
3. Whenever I talked to people who had sent me the invites they said they had been firmly under the impression that I was a LinkedIn user (had joined shortly before, whatever). No one realized that LinkedIn prompted them to invite me to join the network, not just connect on it. My friends know I am not on social networks, and they would not pester me with invitations. But if the impression was that I joined LinkedIn of my own volition, that's another matter.
Conclusions:
A. LinkedIn do not explicitly ask for a user's permission to sift through their contact lists.
B. They use more sophisticated and sinister methods of metadata analysis to connect people than just going through the users' contact lists.
C. They do not tell users that they will be inviting others to join LinkedIn as opposed to join them on LinkedIn, which is misleading.
Now, will anyone tell the lawyers they can sue again?