Google's personalized search now works even when you're not signed in
Personalized search is handy for bringing the sites you actually tend to visit to the top of your search results. That way, Google will know, for example, that you're searching for Six Feet Under, the TV series, and not Six Feet Under, the band. To see how Google customized your results, look for a "view customizations" link at the top right of your search results. If you're more concerned about privacy than convenience, you can opt out of Personalized Search. Otherwise, it's turned on by default.