Morrison and Foerster reports that Japan has just updated its anti-spam law. They write:

Japan has made several substantial changes to the 2005 Anti-Spam Law:
  1. Previously, the law provided for substantial categories of commercial email that were exempt from its rules. These exemptions no longer exist.
  2. Before the amendments, the law established an "opt-out" regime, much like the U.S.'s CAN-SPAM Act.  Japan has decided that this framework is insufficient to curtail unwanted spam and has switched to an "opt-in" regime where recipients must affirmatively agree to receive commercial email before Senders can send it.
  3. Fines for violating the law or relevant regulations have been substantially increased.
They add: Under the New Anti-Spam Law, a Sender may only distribute commercial email if the recipient falls into one of the following categories: Individuals who have notified the Sender in advance that they request or agree to receive commercial email; Individuals who have provided the Sender with their own email addresses; Individuals who have a preexisting business relationship with the Sender; and Individuals (limited to those engaged in for-profit activities) or groups that publicly announce their own email addresses.

That last bit is a little tricky; it sounds like they could be announcing that it would be OK to send somebody commercial email as long as the recipient has "announced" their email address publicly, and if they are engaged in for-profit activities. That's quite a grey area, and it's one I'd recommend avoiding, unless you wanted to be perceived as a spammer.

In short: Opt-in rules!