On this site (including the textboards) adding sage to the email option and responding still bumps the thread to the top of the page so more users will see it. If you actually want to kill a thread just don't reply, that will keep the thread buried.
>>1 Where did that happen? Sage seems to work fine for me, although just like on most imageboard scripts, sage is case sensitive so typing in "Sage" will age/bump the post. Will make sage case-insensitive.