OK, why does any P2P site ever get in trouble? If the standard is only linking and not hosting, why were Napster, Kazaa, Grokster, isohunt, oink, etc. shut down? None of these were hosting content, they just provided links (or the equivalent of links).

The reality is that the courts have recognized that operators who should have a knowledge that the content on their network is almost completely infringing don't have a viable excuse by just saying "we just provide links, we have nothing to do with the actual content". See the Grokster case.

So, here's the question: how much of Google's index is out of copyright, and would it be reasonable to expect Google to know that they are making money off of a catalog that is almost entirely copyrighted content without any license from or compensation to the copyright owners?