Human-powered search engines, better known as Web directories, are popular simply because of the higher quality of links submitted and the caliber of the sites hand-picked to be included in the index. Here are some of the most popular human-powered search engines on the Web.
Eurekster Swickis are "search engines tailored to you and your community. They learn from your users and show what's hot with your people." You, as the creator of the Swicki, have complete and utter control of the search results since YOU are the one who figures out what searches are most relevant to your site, what sites these searches should be pulled from, and how the search engine looks.
The Yahoo Directory is one of the oldest and most exhaustive directories on the Web. What is it, exactly? From the Yahoo Directory Help page: "The Yahoo Directory is a human-created and maintained library of web sites organized into categories and subcategories. Yahoo editors review these sites for potential inclusion in the Directory, and to evaluate the best place to list them."