When is linking a violation of copyright?

Simple enough, I guess. When the owner of the site you are linking to says so.

Now although it is simpler enough to just create a link to an interesting site (That was the original main point of the World Wide Web anyway!) and acknowledging another person's work might be more acceptable than copying and pasting (Go here to see what I mean), I am told that it had to take a trial court to resolve linking issues. Follow this link for more. (Thanks to Xeni Jardin) By then, you will have noticed that I should have used this other one for a more direct link. So what's the beef about links?