I've never used the ignore list before, but I've finally found a reason to.
I'd just like to know how it works. I assume I won't be able to see the person's posts, but will they see mine? What if I create a topic? Can they post in it?
If you add someone to ignore list - nothing changes for them, only for you.
Posts from users in your ignore list will be replace with text "this is post from ignored user XYZ", and you can see his post if you click on that text.
If someone quotes user from your ignore list - you will see his message (only inside quote, posted by other user).
If user from your ignore list made a thread - you will see thread, but inside thread this user posts will be hidden by default (including first post).