http://en.wikipedia.org/wiki/Natto Here is a succinct description of Natto.
Natto is just another way of eating soy beans, the rural people in Japan have been using Natto for centuries, as basically a replacement for meat. In Japan it is sold in small containers, readily available in cafeterias and supermarkets.
My personal view is that the Japanese have the best diet in the world, as long as they can keep the fast food companies at bay, it will remain so. One seldom sees an overweigth person in Japan, and this includes the expatriots.
Many Japanes don't eat Natto, but it has good nutritional benefits, and is easily digested, if one can get it down. The appearaance is like gluey, soft beans, sticking together with strong cob webs or taffy like. I don't suppose one eats Natto for the flavour or taste, but for the nutrient content.
I eat soy beans daily boiled and blended, and have some experience eating Natto, while visiting Japan, I would like to attempt making it, simply for another dietary food.