We visited Hokkaido, which is the north island. Apparently it is quite different from the rest of Japan ... nicer. We would like to return there to see more. Have a look at the Japan section of my journal.
The bit we visited was very receptive to cyclists ... beautiful cycle paths (and some that weren't as lovely) all over the place. Some quite country roads. And quite a few people on bicycles. Generally, the people ride step-through bicycles for utility purposes.
There are campgrounds ... we stayed in a somewhat more rustic one on a lake for a couple nights and spent 3 nights in an Auto Resort campground. The Auto Resort campgrounds are really nice. Very clean and well-kept. There are also Rider Houses, hostels, and hotels.
I took photos of the campgrounds, hostel, paths, and other things, and posted them on Flickr.
The cost was about what we would have paid for things in Australia, and the Yen was such that if something cost 1000 Yen that was approx. the equivalent to $10 Australian. So a campground might cost 2400 Yen or $24/night. A hotel might run 11000 Yen or $110/night. Food in the supermarkets was also about the same as we might pay in Australia.
One note about the train, apparently you can only take your bicycle on the train on Hokkaido if it is boxed. Unlike the UK and other parts of Europe, you can't just roll your bicycle onto the train. We considered using the train, but boxing the bicycles would have been a pain.
And speaking of boxing the bicycles, we bought Qantas boxes in Melbourne when we started, and used them till we arrived in London. We were able to store them at hotels at the start and finish of our time in Hong Kong (we just left the bicycles in the boxes there), Taiwan, and Japan. But once we arrived in London, we had to let the boxes go. It was rather sad because those boxes served us well, and were still in decent shape. But we're flying out of Paris, so we couldn't haul boxes around with us for 3 months.
We haven't used the alarm yet, and actually need to look up the instructions for it again.