If you're buying any type of electronics, besides making sure they work in the US, also check out prices of similar items in the US before you go over so you know if you're getting a good 'deal', especially since the Yen still kicks the $$ butt.
mjm lives in Tokyo, so you might want to drop him a PM. There's a musuem on top of the Maori Tower you can go to, as well as top of the tower itself for some fab views. It's in the Ropaangi Hills area (sp?), which has the Grand Hyatt, the tower, shops, concert area, residential, etc.
And of course the Fish Market is a definite MUST!!! Just know it's a very very early am. And of course the tradition is to have fresh sushi/beer right after at one of the nearby places.
Have a good time. Cheers.
Sharon