Yahoo has released beta version 2.0 of their My Web search engine . What's different about My Web? Well, Yahoo is calling it a "social search engine," which, they claim, "complements web search by enabling users to search the knowledge and expertise of their friends and community in addition to the web." This could be a very useful tool for reference librarians who would like to save useful searches and quickly find that great answer from last week. More from the Yahoo blog post  announcement:
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.
If this interests you, also check out Google's personalized search .