Well, though I don't live in Japan, I think there's a place where Canonites should find time and visit if they ever drop by Tokyo - the Canon S. Tower near Shinagawa Station.
In fact, it was pure chance that I ended up discovering the building after calling off a one-day visit to Kamakura and ending up exploring the area around Shinagawa Station.
To get to the Canon Tower, exit the JR Shinagawa station (on the side where you see a bunch of towering skyscrapers and huge multi-story walkway/corridor/skybridge complex) and it's a walk of about 15 minutes or so. If you get lost, just look at the map guide along the path.
What's there inside the building? Well, I didn't have much time to explore beyond the entrance, but I noticed a cafe, a small gallery (there was an exhibition on railway photos when I was there last year), a product center, and a demo section for most of the big-white lenses (yeah, the 500mm and 600mm were there - you can test these telescopic muscles by peeping through the camera at people drinking coffee at the cafe on the other side).
Anyways, its a place to go if you ever wander by the area