Some selected excerpts:
Search engines in the future will become better for a lot of different reasons, but one of the reasons will be that we understand the user better ... Search engines will have become more personalized.At the end of the interview, Marissa also indicated that they will not be personalizing advertising any time soon; the focus is on using individual searcher history to improve relevance, not to improve revenue directly.
We've been working on personalized search now for almost 4 years. It goes back to the Kaltix acquisition .... They were on the cutting edge of how personalization would be done on the web, and they were capable of looking at things like a searcher’s history and their past clicks, their past searches, the websites that matter to them.
We acquired them in 2003 and we've worked for some time since to outfit our production system to be capable of doing that [personalization] computation and holding a vector for each user in parallel to the base [vector].
Our standards are really high. We only want to offer personalized search if it offers a huge amount of end user benefit ... We're very comfortable and confident in the relevance seen from those technologies.
Overall, we really feel that personalized search is something that holds a lot of promise, and we're not exactly sure of the signals that will yield the best results. We know that search history, your clicks and your searches together provide a really rich set of signals ... It's a matter of understanding how... The more signals that you have and the more data you have about the user, the better it gets.
See also some of the papers -- "Scaling Personalized Web Search" and "An Analytical Comparison of Approaches to Personalizing PageRank" -- by the Kaltix folks.
See also my Feb 2007 post, "Google expands personalization", and my June 2005 post, "More on Google personalized search".