Yesterday I told you about Google’s Personalized Search. Today Yahoo! announces they are working on Social Search and answers the question “How Is Social Search Different?”

Social search complements web search, which is driven by publishers and web sites, by providing a better search experience that is powered by people and communities. Flickr is a great example of this power applied to photos and image search.

Much like links and anchor text enabled major improvements in web search by becoming a new source of authority for search engines, people and trust networks are now an additional source of authority for social search engines. In the same way that blogs and RSS are empowering individuals to participate in publishing, individuals and communities can now participate in search, using tools like My Web 2.0 that let them define what is valuable to them and their community.

Over time, we envision communities using My Web to build their own search engines to capture and make accessible the knowledge of their community — search engines populated with the collective experience of a group of medical researchers, a community of PHP experts, a bird watching club, or members of a structural engineering consulting firm.