As Kkim correctly stated, the ignore list only affects the member who chooses to use the feature. In a sense, that member sees a view of the site, with all of the content created by the ignored user blanked out. The member won't see posts from that user, won't see PM's (or get PM notifications) from PM's sent to them by that user, and for all intents and purposes, it's as if that user doesn't exist on their view of the board. The one exception is within quoted posts. If you have someone on ignore, but somebody else quotes a post of theirs within their own posts, you will in fact see their post content (since the poster of that content isn't on your ignore list as well).
From the ignored member's perspective, nothing changes. They can still see everything that they could before on the site, they can still send PM's to anyone (though the ones they send to people who are ignoring them just go in a black hole and are never delivered), and they really have no idea whether or not somebody else has them on the ignore list.
What all this means is that anyone is free to experiment with the ignore function to clean up their own particular view of this site, with zero consequences on what anybody else sees. The only caveat is that to make this work, it's ill advised to continue to quote all the text (or any of the text) from any particular troublesome users, as then anyone who happens to have them on ignore still is subjected to that content. I don't think we have any folks on this site that are truly so over the top to be offensive to all and hit the double-digit ignore threshold, but the site's young. We might get there.
