when does moral responsibility kick in, and what action can be taken...

[Gooberlx2]

...concerning threads like this one and so many others like it in message boards across the 'net?

I have no idea if there's any legal obligation for the site owners to take action, but when warning signs become so clear (I'm no psychologist, so I'm not suggesting anything about the example thread or poster) that action should be taken, and if the site owners chose to do so, how could they help? The same would apply to any poster who said he was going to kill his family, or a poster bragging about dealing crack. Where's the line?