I've known about the YubiKey for some time and it seems like a good option for multifactor authentication given some of the reviews online and its reputation. For some added assurances, Google and Facebook use YubiKey.
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .