The key challenge is personalization

Paul La Monica at CNN reports on Yahoo co-founder Jerry Yang's speech at the Search Engine Strategies conference. An excerpt on personalization:

[Yang] also said that the key challenge for Yahoo! and all search companies going forward will be to find ways to increased the personalization of results, i.e. making sure that a user truly finds what he or she is looking for when typing in a keyword search.

"The relevance of search is still the Holy Grail for any search application," Yang said.

With only one generalized relevance rank, further improvements to search quality become increasingly difficult because people disagree on how relevant a particular page is to a particular search.

At some point, to get further improvements, relevance rank will have to be customized to each person's definition of relevance. When that happens, you have personalized search.