This allows Google to ... [tap] into your current browsing behavior to try to determine what's on your mind right now ... It helps Google interpret just the kind of site you want to see, given your behavior at the present time.Search is about finding. Recommendations are about discovering.
[Google can] find similar sites you may have never considered, based on the characteristics of the sites you have been visiting ... It's not just providing you a shortcut to sites you are already aware of, it's in making you aware of new sites you never knew existed, ranked and prioritized according to the PageRank algorithm.
The promise of personalization is moving Google to be a true recommendation engine.
It is hard to find something if you do not know it exists. It is hard to find something if you cannot easily say exactly what you want.
Personalization can help you discover information you would not have found on your own, sites you never knew existed, based on your past behavior and interests. Personalization and recommendations aid discovery.
Update: A few days later, Gord Hotchkiss publishes an interview on personalization with Googlers Marissa Mayer and Sep Kamvar.
Update: In yet another article, Gord Hotchkiss says:
As Sep and his team begin to refine personalization, expect it to be aggressively rolled into multiple aspects of your Google experience.
[Personalization is] the engine that will power the future of Google for the foreseeable future. It will eventually surpass the PageRank algorithm in importance, giving Google the ability to match content to very specific and unique user intent on the fly.