This news is swarming all over korean and japanese sites right now.
Larger update? PlayStation network in Japan is switched off
05.03.07 - Sony communicates that the Japanese PlayStation network is temporarily switched off because of maintenance work.
To 07.03.07 (Wednesday) it is not attainable by 07:00 clock to 11:00 clock (local time Japan). The disconnection refers to a larger update, which could possibly be accomplished at this time.