One of the boating websites I frequent has been the victim of one of these "denial of service" attacks, as you so aptly name them. Like the Zone, it is a by-subscription-only site with public component, but one of the old-timers there (whose politics were unknown to everyone else there until recently) suddenly started to flood the site with partisan comments. At first he got some response, both pro and con, but soon the others, on both left and right, got rather fed up with his crap, and told him to take it somewhere else. He continued, using the usual excuses ("political considerations affect boating", and "this is still a free country and I have my first amendment rights"). The others eventually responded by refusing to answer any of his political posts.

I will not indicate on which side of the political spectrum this guy was coming from, since it really doesn't matter. As far as my own politics were concerned, I have always kept them quiet from the group because I depend on them for intelligence from the sailing world, and as a source of technical expertise to help me write my articles. I cannot afford to make any enemies there. These are all potential readers.

The site management eventually moved the controversial posts to a forum closed to non-subscribers, and without an audience, the offender predictably shut up.