As I wrote long ago, I seriously doubt Facebook can surpass Mixi or Gree in Japan. The Japanese like their privacy and Facebook doesn't address these concerns nearly enough.
I suspect that if Facebook cannot dethroned either, it will be a failure in this country.
Actually, with how much of a problem hacking and stealing identities is these days, I am amazed at just how many people in the west put up so much personal information on Facebook.
Once again, I have found a recent article that supports my beliefs about Facebook not becoming number one in Japan and how the can't do so as the cultural differences are too great.
Let's face it, Mixi and Gree were made in Japan, they completely understand the Japanese psyche. Facebook doesn't. Also, one of Facebook's biggest sales points is that it let's you connect with people overseas. That is not a big point of appeal to the Japanese.