I don't think it's quite as successful as the "Shining" trailer, and I have a theory as to why. Kubrick didn't film "The Shining" like a typical horror movie. For the most part, the film is brightly lit, and in deep focus--not the usual dark, things-lurking-in-the-shadows photography used in most horror flicks. Therefore, it's kind of easy to make the movie look like a romantic comedy.
"Mary Poppins" is also brightly lit, and colorful, and the action in it is a little too goofy-looking, and thus it's a tad difficult to make the movie look scary. Although I think whoever did this trailer made an admirable effort.
[Via Boing Boing]