For Google, social search would involve tying a few pieces together of what it’s already doing. Google already personalizes results for registered users based on their previous searches. It could further personalize search results based on groups of registered users– namely, those on a user’s Google Talk list. Now, following this line of logic, assume that this group of registered users is clustered largely around one or two common themes, such as technologists in the Pacific Northwest or Bible Belt NASCAR fans or Binghamton University college students. With personalized search results based on a presumably like-minded community of users, it all starts to resemble vertical search, a concept Eurekster acknowledges about its swickis.
To recap, personalized search becomes social search. Social search becomes vertical search. All of this with the goal of making search results more relevant.