Collaborative Web Search (CWS) seeks to exploit the high degree of natural query repetition and result selection regularity that is prevalent among communities of searchers. CWS reuses the search experiences of community members, to promote results that have previously been judged relevant for queries. This facilitates a better response to the type of vague queries that are commonplace in Web search and allows a generic search engine to adapt to the preferences of communities of individuals. CWS contemplates a society of search communities, each with its own repository of experience. In this paper we describe and evaluate a new technique for leveraging the search experiences of related communities as sources of additional search knowledge.