The Terms of Service was recently updated to include a clause that says only Japanese people may play. The game's producer, Sakai, elaborated on this his weblog and says that as long you behave, you should be fine.
Apparently there have been lots of rude English players and hackers on the server.
I stopped at about level 25. The game is fun but I think I will enjoy it more once it is completely in English (the patch is nice though). I have other games to play right now...