What it is
Social search is the broadest of the new search categories. Searchengineland.com Editor-In-Chief Danny Sullivan, a search engine analyst for the last 12 years, defines social search as "Any kind of search that's involving humans in some way and, in particular, humans that have a network of friends or associates."
Google Vice President Marissa Mayer in January described this type of search to VentureBeat as attempting to "leverage a social connection to try and get a piece of information that would be better than what you'd come up with on your own."
At its most basic level, social search looks something like the Amazon.com model of recommendation. Results for a book or CD search on Amazon return with a note that "Customers Who Bought This Item Also Bought…" Amazon tracks user behavior to generate suggestions that might help guide other purchasers.
More sophisticated social search sites aim to combine these overarching recommendation engines with social networking. Delver, one of the newest arrivals to the social search scene, combines user information (name, email, social network profiles, etc.) with search requests to tailor its results to the individual preferences and habits of the person conducting the search.
More established social search sites such as Digg and del.icio.us rely on users to rank news stories or blog posts to give visitors an overview of the moment's most popular conversations across the web. Sites such as Mahalo pay users to filter through search results and eliminate fluff.
Who's doing it
Delver (currently in private beta), Digg, del.icio.us, Eurekster, FriendFeed, Mahalo, Mechanical Zoo, StumbleUpon
Why you should care
Social search sites can offer real value to marketers. Though direct marketing and advertising opportunities remain limited across social search sites, these engines allow marketers to easily track user communities and conversations, producing knowledge that can ultimately drive traffic to brand sites.
Sullivan points to digital marketing company 10e20's campaign for Virgin Vacations as the archetypal social search success story. Virgin Vacations produced a text and video story about the world's best subway systems. Thanks to a little viral marketing, users of Digg, del.icio.us and StumbleUpon picked up on the story, resulting in a huge increase in traffic to virgin-vacations.com.