How far does this 'de-personalization' go? Do they still factor in user agent, screen size, geography etc.? I would guess that even an anonymized Google search is still fairly 'personal'.
You can always compare with http://scroogle.org/. Though I sometimes wonder if its results have been "personalized" for a collective mind.
That means no results from your friends, no private information and no personalization of results based on your Web History. This toggle button works for an individual search session, but you can also make this the default in your Search Settings. We provide separate control in Search Settings over other contextual signals we use, including location and language.
If you just log out of your google account search should be fully 'de-personalized' right?
That would be up to Google. They still know your IP address, general location, browser, OS, etc. and can use that to "personalize" your search results.
That can still be 5 different people in one house. Or several hundred in a neighborhood.
Cookies can solve that. If that's how it works is another question.