A meta-data file over VLC player where people can add additional information about a movie so that others watching the movie can skip right to that part. Say, a movie has a few funny scenes, or action or even sex, and you only are bothered to watch those parts. Then you can use this file to see at which time period these scenes exist in the movie, and jump right into it.

Not exactly a startup idea, but something that can be useful, eh?