[clhodapp]

Common techniques like relative paths will allow the proxy-cache to see much deeper into a site than the end user is aware. The url bar might say that you're on some site you trust but your traffic may all still be openly readable by Google (or some other proxy). Of course, Google is always going to know about links that users click in its search result list and a huge number of sites blindly run Google (or other third party) scripts anyway but this opens up a new vector for Google to see into your traffic.