The military has been using surveillance camera drones for years, now the police and the average citizen has access to this technology. Like any technology how it will be exploited for good or bad, only time can tell how it will be used or abused.
Watch the video like the one below to see what awesome things can be done with this technology, but you might also see the potential for how the technology can be abused. For example, it gives anyone access to view in to places they might not of had access to before.
I am not a legal expert in any way, but as I understand the law about privacy, every person has a reasonable expectation of privacy unless they are in a public place (more information).