Yay! Using the info here, I finally liberated myself from that incessant LinkedIn spam:
LinkedIn Customer Support Message
Subject: Add My Email To Do Not Contact List
I truly apologize for the delay in my response.
Per your request, I've added your email@example.com email address to
our "do not contact" list.
You will no longer receive any email from LinkedIn or our members on this
email address. If you decide at a later date that you want to set up a
LinkedIn account, you will need to first contact
us to have your email address removed from the “do not contact” list.
If you have further questions, please feel free to reply to this message.
LinkedIn Customer Service
Member Comment: Karen Nakamura 01/17/2012 01:33
Please add my e-mail to your do not contact list. I have no wish to ever use linkedin.