Interesting comment on Battelle Media (excerpted from Rex's blog):
If A9 incorporates the collaborative filtering algorithms that power Amazon's predictive recommendations to customers, it will (and I know this from very, very expensive first-hand experience) produce search results that will astound the user. Just think about it: Your search results will be filtered first by Google algorithms and then through Amazon's collaborative filtering algorithms.
This oversimplifies the difficulties with personalizing web search, but it's definitely on the right track.
I have little doubt that A9 will try to do personalized search. But I have my doubts about whether they will succeed. The team at A9 has expertise in search, not personalization. The people who developed Amazon.com's collaborative filtering algorithms are not at A9.