Watching the watchmen

We're all aware of the "Big Brother" factor in our lives. Surveillance cameras are found in many spaces we visit through our day, i.e. banks, stores, schools, hospitals; and in some cities, even streets and parks.
According to an article on WorldChanging, "In 2004, NYC police arrested nearly 2,000 people during demonstrations around the Republican National Convention." Footage from the city's many cameras were used to prosecute those arrested. But the police weren't the only ones armed with video cameras. Footage filmed by those on the street, unaffiliated with authorities, were used to successfully defend unfair charges. "It turned out that prosecutors selectively edited the official video record to prove their cases, and police officers repeatedly misrepresented the protest events at trial. 91% of the charges were dropped or with not guilty verdicts."
Today, video cameras are affordable for many, and the power of recorded actions can be used in favor of fair treatment of people. Even cell phones are capable of recording good-quality footage that can help us fight oppressive law enforcement. In what other ways can affordable video help our society? (other than cats playing pianos on YouTube.)