Google's personalized search

Google's personalized search has left Google Labs and is now available to users on 38 Google domains in addition to Google.com.
Google's personalized search reorders search results based on your history of past searches, giving more weight to topics that interest you.
Google Personalized Search that opened last year let you create a profile used to customize your results. By selecting categories, you could tell Google you were interested in things like movies, radio and music. Then by using a slider, you could "personalize" your results to skew them toward your particular interest areas.
Google hails Personalized Search Results. In it, I explained that Google was classifying pages across the web into topics. The "personal" results were simply those skewed more toward the topics areas you were interested in, a profile you had to manually create.
In the new system, a profile is created automatically. As said, exactly how isn't explained yet by Google. But almost certainly, it's measuring what you click on and then skewing your results over time to favor sites that fall in particular topics areas seems part of it.