Loosing all the photos from Japan...
The greatest disappointment I ever had in my travels was when my photo films about Tokyo Yokohama and Fuji were spoiled in a photo laboratory after I came back home.
It happened in 1993. I had an analog camera with two photo films for making slides (72 stills).
You remember we had to use sparingly every still then before making every shot. And I was very glad that I had taken photos of Ginza, Akihabara, the Imperial Palace, the Edo Museum, and Disneyland in Tokyo, Iokohama Bay and Bridge, the Fuji Mountain...
So you can imagine my disappointment when in Moscow I have been told that my photo films were empty without any picture... I had nothing to do besides coming back to Japan and repeat taking photos... 18 years passed since then, and I wouldn't be able to come back to Tokyo yet.
I hadn't a video camera then but a friend of mine had just bought a new Sony. I could ask him to give it to me for making a film about Japan but I felt shy... I was mistaken. And I feel sorry for it till now...
I cannot think yet of a danger or real warning about this place. I can only think that as this place is very popular among domestic and foreign tourists that you should be aware of it that they will be everywhere with their camera's :)