Let me highlight this tidbit on the results of an eye tracking study:
The personalized [search results] ... doubled the performance (click throughs).That reminds me of what Googler Marissa Mayer once said:
[Personalization is] one of the biggest relevance advances in the past few years.Update: More details on the eyetracking study.
Personalization doesn't affect all results, but when it does it makes results dramatically better.
Update: Even more details on the eyetracking study.