While people helping to hunt for Fossett and Gray are volunteers, other Mechanical Turk projects pay participants, usually less than US$0.25 per task.

Mechanical Turk isn't the only online service that relies on human intelligence. ChaCha.com, a search engine launched last year, uses human "guides" to provide search results. A user inserts a search term and a remote worker searches for the answer, sending links to Web pages back to the user. The guide may be an expert in the subject the user is searching for so may be able to find better results than other search engines, according to ChaCha.

Mahalo.com is another search site that uses people to compile results for common search terms. Workers weed out spam sites, pages with overbearing advertising and sites that use information without giving appropriate credit to the source.