The NY Times recently ran an article on the ultra-nationalist group calling themselves the ネット極右 (Net Kyoku/Net Far Right) whose members have been harassing various foreigners and spreading their racist messages of intolerance and hate.
http://www.nytimes.com/2010/08/29/wo...a/29japan.html
Definitely a very scary group of Right-Wingers who seem to be exploiting the internet to coordinate their rallies and target individuals. You'd think these guys would have something better to do than scapegoating foreigners for all the social/economic problems facing Japan.