I think this is the essence of the matter: you have to protect your site. No-one else (including Google) is going to do it for you.
I think we could class most sabotage attempts as Search Engine Denial of Service (SEDOS, catchy, huh?): crowd out, or push down the opposition.
To me, it's just a variant of hacking: mostly affects high profile targets, no one is ever totally safe, there are large networks out there.
The wording of (and edits to) Google's guidelines have always been a subject of interest to me. The recent change: Google are getting a lot of emails from people worried about who links to them.