Together the small contributions can have significant value. Wikipedia is the most common example. Sentence by sentence volunteers have created an encyclopedia more comprehensive and just as accurate as Britannica. Many online stores use crowdsourcing to create and rank product reviews. A newspaper in the UK has created a system to let the public review over half a million pages of government expense accounts. So far, the politicians will be paying back £478,000 for inappropriate expenses.
Amazon has built a programming interface and service called MTurk that allows companies to submit tasks that require human effort, receive the completed work, test for quality and then pay for the work. This is being used for everything from identifying the addresses in drive-by photographs, to translating documents, to audio transcription. The system gives you access to a very large number of workers from around the world—all paid on a per piece basis with appropriate quality controls and error checking.