Increasingly, social bookmarking websites are being used as a surrogate search engine. Yahoo, Google, and the other search engines are extremely useful tools, but they can also bring back so many websites that it becomes a real chore to wade through the useless sites to find that needle in the haystack.
The reason for this is the basic way that most search engines operate. They "crawl" the web by having a computer scan websites and pick out keywords to index for a search. The computer then catalogues the links on the page and moves to those web pages to index and catalogue, and so on, and so forth until they've "crawled" the web.
This makes them a very valuable tool in some instances, and a bit unwieldy in other instances. If you don't search just right, you might not get very good results.
On the other hand, websites on a social bookmarking site are added by people, not computers. Someone found the website interesting and wanted to save it for later or send it to a friend. You can even see how many people found the website interesting enough to add to their bookmarks, which can give you a basic idea of how useful the website really is -- something a computer wouldn't be able to do.
One of the key aspects of Web 2.0 is human interaction. It is this human component that is taking the Internet to the next level by leveraging the strengths of the human mind with the strengths of a computer's processing power. While a computer is great at reading large amounts of data and searching for defined patterns, the human mind can spot undefined patterns and, more importantly, can detect quality.
It is this ability to judge the quality of a website that makes social bookmarking a great resource for searching the web. Browsing through a traditional search engine's results can sometimes be like finding a needle in a haystack. By combining the search with the popularity of the results, we get a haystack ordered with needle-like results first.
