Brett Tabke, WebmasterWorld founder questions in a WebmasterWorld thread – "I think I have been logged into Google when I hit google.com before and gotten the "classic homepage".
Today, I just went there and I got my personalized Google page as the http://www.google.com homepage.
Have they been doing this for awhile? "
It seems if you are signed in and visit Google's Personalized home page and then return to Google.com, Google will take you back to the personalized home page. Clicking 'Classic Home' link is the only way to get back to the main search page, Google.com