Even though it never had been my cup of tea, I do recognize Wubi's advantages as being a very useful tool for Windows users with only basic computer skills, because of its convenience.
No need to burn a CD or create an installing-USB, just download it from the Ubuntu homepage and install Ubuntu like any other windows application.
Another benefit is that it's totally safe. New Linux users can freely tinker around and customize their system, without any fear, because with Wubi, Ubuntu is installed as an application so it's totally safe to mess around and if something bad happens, they just have to uninstall it and their data and Windows will still remain untouched.