[voice]
It seems as if Christian holidays are commonly celebrated in many places, though usually sans the religious aspects. It's certainly that way with certain holidays in Japan.
As for the Japanese people, many of them don't identify with a specific religion. Many of the beliefs may draw upon aspects of Shintoism and Buddhism, as well as other traditional folklore. Of course, that's not to say that there's aren't people who strictly follow those religions. Most others, however, such as Christianity, Islam and others fall into the minority. It's certainly very different than many other places in the world that rely heavily on their faiths. [tl;dr, Mitsuru has it.]