Movie trailers are an interesting breed. No matter how crummy a movie may be, they always seem to make a movie look good. It's their job to build hype and get people excited about seeing the actual film. They are definitely an editors medium: simply gather the best bits of a film, string them together, an presto! A mini movie!
I'm not saying that those who create trailers are hacks who can't get a real job in Hollywood. It's a credit to these artists that they often make a terrible movie look interesting (The Island), drawing us to the theater with false hopes ending in letdown. Sometimes a trailer will make a great film look really ordinary (L.A. Confidential), and while you don't exactly run to the theater, it's a nice surprise when you get there.
YouTube's blueyoda has taken an interesting approach to the movie trailer, creating a sixty second version of various movies. In essence this is a trailer, but I think it's a bit more. There is no slick music covering the entire piece, and no title cards linking scenes together. They are creative Reader's Digest versions of the full movie that often capture the essence of said film with humor, style and obvious love for the movies.