In a social bookmarking system, users store links to web pages that they find useful. These lists can be made accessible by the owner to other users of that bookmarking system. The users categorize their resources by the use of informally assigned, user-defined keywords or tags. Other users with similar interests can view the links in the system by topic, category, or tags. The results of these searches are usually more useful to the user than those conducted using traditional search engines on the web.
An example of such a search, using the tag "web2fordev" can be seen at "del.icio.us/web2fordev".
"Technorati" and "del.icio.us" are examples of social bookmarking sites. Click here to read the "del.icio.us" explanation of social bookmarking. Another example is "Digg", which is described as follows in Wikipedia:
"Digg is a community-based website with an emphasis on technology and science articles, recently expanding to a broader range of categories such as politics and entertainment. It combines social bookmarking, blogging, and syndication with a form of non-hierarchical, democratic editorial control. News stories and websites are submitted by users, and then promoted to the front page through a user-based ranking system. This differs from the hierarchical editorial system that many other news sites employ." http://en.wikipedia.org/wiki/Digg
Some social bookmarking tools enable users to bookmark a site in multiple social bookmarking sites at once, e.g., the "socialmarker" shown below and also in the left hand column of this site.