A9 (Amazon search)
April 15, 2004: Amazon has launched a (beta) search engine called A9. Since you're already a registered member of Amazon, they can do things like saving your most recent searches and noting when you've followed a given result link. Of course Yahoo could do the same, but probably has figured that privacy concerns might keep people from using the search engine if it's tracking their search behavior, e.g. "Your most recent search: 'Britney Spears naked'."