The big Social Networking site in Japan is called Mixi. Don't bother trying to join it, you'll need to be invited by a current member in order to get in.
I know of a few people who do Facebook in Japan. I'd have to say that, amongst the people I know, that the ratio of Facbook users versus Mixi users is about 10 to 1 in favor of Mixi.
The Japanese people like things that allow them to have their own "clubs" Mixi is much better suited for that than Facebook is. Also Mixi allows people to use pen names. That is a critical issue in Mixi's success in Japan; Japanese people are much more strict about their privacy and do not like to tell the world who they are and where they live.
Mixi fits the bill for the Japanese.
The Japan Times confirms this:
Facebook is also not convenient to use on cellphones in Japan. When you consider the problems with privacy and that 90% of all cellphone users in Japan do not have a computer at home, then you can see where Facebook has big problems in Japan.... Not to mention that their "Spokesman" is too busy to answer a phone call or his e-mail for a comment from one of the oldest and most famous newspapers in Japan.
Hello Facebook? Yeah, what's the purpose of having a "Spokesman" that doesn't answer his email or phone calls? I reckon this is indicative of why your business hasn't really taken off here amongst the Japanese. Hire a new spokesman... Preferably one who speaks Japanese and understands the customs and business manners of Japan.