I've lived in Japan on and off since 1999, and I'd say that the States beats Japan for price and selection in all PC hardware.
However, electronics made in Japan are usualy released domesticaly first, for testing and whatnot. And some electronics are never taken to the export market. So if you're into stereo/DJ gear or plasma TVs or that kind of thing, Japan gets it first. However, it isn't cheap. And Akihabara in Tokyo is the best place for electronics.
I think one of the best deals going right now is cell phones. Cell phones here are years ahead of anywhere else. I have a buddy that regularly buys a few high end models, takes them back to Canada, and reprograms them somehow for use in Canada, and sells them on EBay at a markup. Apparently it is only possible with certain models.
Another popular item recently were the Sony PS3 and Nintendo Wii. For quite a while you can just walk into any ToysRus and pick one up for about $400 and $200 respectivley, while I heard availability has been not too great back home.
The ps3 is region-free and the blu-ray region coding should be the same for north america and japan. however, the dvd coding is locked as is the backward compatibility. US ps2 games and dvds are useless on a jp ps3.
the wii is totally region-locked, and the system menu itself cannot even be changed to english. there are plans by datel for a region-opening disc, but you will need to use it every time you start a US region game on the jp system. The controlle is really neat to use.
I've heard that its not really worth getting either right now though, as the game library will be really poor for about 6-12 months.
But Okinawa, best bet is to bring you back that guy from The Karate Kid.