The last straw was the one where they requested your email login details, and proceeded to spam your contacts with join requests. What kind of a prick of a company does that?
I guess they factored in the people that'd pay attention to that kind of scumbaggery, and those that wouldn't and figured they'd end up on top. Guess they did too. You're a product, not a customer, when you're on LinkedIn, much the same as Facebook.
The nail in the coffin for me has been recruitment agencies stressing I should be on it - any advice from the vampires like that is a good sign you should be doing the polar opposite.