Yes.
Click on your profile, then on 'Modify Profile', move your mouse down to 'Buddies / Ignore list' and click on it. Then 'Edit Ignore List'.
Type in the name of the person you want to block and when you confirm it, what will happen is that it will show the person has posted in the thread, but not what they said. It will provide a link inside the post that you can click to choose to view the content. It will also block PM's from that person.
