I vehemently disagree with you here. Content mills horribly abuse writers and make it difficult for people who have spent years in this field to get a fair wage due to the expectation that companies can pay less to get more. Also, writers who start out here often get stuck in a rut and can’t evolve past the oDesk stage. All around bad news and not recommended for anyone who wants an actual career in writing.
These little jobs are done by people who log on to a company’s site and choose tasks, which could be as simple as clicking a link. Amazon's Mechanical Turk is one of the most well-known sites of this type. Also, there are crowdsourcing projects, which are similar to data entry, where companies engage an army of virtual workers to each do one small part of a larger project.