I seem to be getting random invites from people I "kind-of" know via some site called Notchup. No clue what this is, and the invites are all very boilerplate in nature. And there's some promise of getting paid for job interviews. And from talking to other folks, it sounds like somehow they get your contact info from LinkedIn. (Perhaps from a user giving up their username and password legitimately -- so likely not LinkedIn's fault -- but potentially this means Notchup is providing a tool for users to harvest their LinkedIn address book. Yuck.)
Then there's the WHOIS information for Notchup. See how it's owned by Domains by Proxy? That means the true owner of the domain doesn't want you to be able to tell who they are. No business name, no street address, no contact info.
That's who people are giving their contact info to? A site where the true owners of the site don't want you to know who they are?
Yeah, I don't think I'll be signing up, just yet.
(More good points to think about here.)