I have MLB.com and love it. The blackouts suck if you follow a local team. I follow the Red Sox from Florida, so I'm only blacked out of Red Sox at Devil Rays or Marlins games.
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 .