Raul Valdes-Perez (CEO of Vivisimo) has a CNet article attacking personalized web search and touting the virtues of document clustering.
Raul makes some excellent points on the difficulties of doing personalized web search well. He says people's interests are fleeting and noisy. Raul says it's difficult to accurately infer interests from clickstream data, which is also noisy and imprecise.
It's true that personalized search is challenging. But Raul criticism is overstated. If personalized search learns immediately in response to new data, it can react to people's immediate goals and interests, even if they differ from their long-term behavior. If the personalization helps in more cases than it hurts, then the personalization has value, even if the data is noisy and the assumptions made from the data are speculative.
Raul's solution is to give up on personalized search and do document clustering instead. Vivisimo's Clusty is an excellent clustering web search -- if you haven't tried it, go try it, it's great -- but it requires effort. Users have to refine their query repeatedly using the clusters to find what they want.
People are lazy. They want what they want and they want it now. Google recognizes this, providing an "I'm feeling lucky" button that just sends you to the top search result immediately. They recognize that it's better to just find what the searcher wants on the first try, no refining, no effort.
Personalized search offers improvements to relevance rank by recognizing that relevance differs from individual to individual. Personalized search makes it more likely that you find what you need on the first try.