The big four in social search are Flickr, YouTube, Technorati, and They specialize respectively in pictures, videos, blog entries, and Web sites, and each lets users tag and store material for their own use and also search to find what others have tagged. Their principal advantage is that each of them has more users than its rival sites do. For some online activities, broader participation is not always a plus: the more members of the “Google Earth Community” who apply comments to an aerial photo, for example, the harder it can be to make out either the scenery or the other comments. But the whole idea of social search is that each new assessment of a site’s value or content helps other users to find more precisely what they want.

Ma.gnolia does all that does, plus stores page contents for viewing if the original link stops working, plus gives users more tools for rating and describing a site. Furl makes it easy to export lists of tagged sites, for research purposes. Wink emphasizes the creation of small communities of shared interests. TagJag is a kind of master search engine for all other search systems. There are hundreds more. On, I (as user AtlanticTech) have tagged a list of these and the other sites I’ve found most valuable, and of the articles and reviews worth paying attention to. You can find it there. —J.F.