[ehsankia]

How so? The web package comes from the real source you see. The only reason Google needed to serve the content from its own domain is because of security and limitation of content delivery. But with this, they can serve you a "package" that's identical to what you get from the source.

[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.