Google has extended its personalized search functionality to users who are not even signed in. This goes for Google users around the world, in over 40 languages. What this means is that when you search with Google, it will provide results that are aimed at higher relevancy to the individual user, as opposed to relevancy for the average person.

http://www.webpronews.com/topnews/2009/12/07/google-personalizes-everybodys-searches