YouTube and online video
YouTube is a web site where users are able to upload videos to their own account and share them with the community. One does not need a YouTube account in order to watch videos on the site. Users are able to rate, favorite, comment, and "flag" videos for inappropriate content.
Some Youtube videos are only available to registered users who claim to be 18 or older. However, there is no way the site can control whether the information a given user provides is accurate.
Outside of the normal user account, is the Director account, which grants the user special abilities, such as being able to post videos longer than that allowed to the regular user. You're also allowed to have a customized badge, and your username displays Director underneath at all times.
When watching a video, related videos (determined by title and tags that the person who uploaded the video chooses) appear on the screen.
YouTube has a strict copyright policy and does not allow for any copyrighted material to be uploaded to the site. If such videos are found they are immediately taken down and the user who posted the video can potentially have their account frozen. There is a small section on "Fair Use", but it is essentially there to direct uploaders away from it.
Other streaming video sites such as Revver and now even Deviant Art, feature several new and innovative features regarding copyright. Revver's entire upload system is based around the "Fair Use Doctrine." They highly encourage creativity via remix videos and the like. Deviant Art on the other hand does not allow for copyright material to be uploaded. However, the user, upon uploading their video, is given a choice as to which copyright they want on their property. Some options allow for other users taking the video and changing it, others state that the user doesn't want their video altered.