This is a really fresh topic.
I've just received an email from LinkedIn, which I'm sure many of you have received, and received it plenty of times in the past.
Ok, why do I say spam? It is really a rude word on the internet, I know.
When you register to Linkedin, never push the "Continue" button. If you do so, Linkedin will send a letter to all your contacts, and not only once, but 3 times.
This is what your non Linkedin member contacts will call spamming. Which is actually spamming :(
Could be a solution to have a special email address dedicated to Linkedin only.
For instance firstname.lastname@example.org