Hugh Macleod writes that Microsoft should buy Facebook because "all search begins and ends with people, not algorithms". I don't know where this diagram came from, but it expresses the evolution of search pretty perfectly — from portal to search engine to social network.
One of Hugh's commentors took issue with his view, stating that search and recommendation are not necessarily the same thing. Surely they are similar. Google's relevance algorithm is a voting algorithm based on how many other sites link. It's a mathematical model of the meatspace recommendation algorithm that Facebook represents.