I've heard from friends who have tried it here that it was basically all gristle. It's not terribly popular here, either--essentially, it was a food that a lot of people ate during the Occupation because the Allies (read: the States) wouldn't give anyone food because "they brought it on themselves." They did give schoolchildren powdered skim milk to drink, though; my old advisor remembered eating powdered skim milk, rice, and whale meat as a child back then because that was what they had. I believe it was also a "desperate times, desperate measures" food in certain locales before that, but I haven't investigated too closely. People who eat it now are basically probably doing it for neonationalist reasons.

I don't eat it because it's environmentally and ethically wrong, and because I find the Japanese government's obstinate hypocrisy on the issue especially frustrating. It's one of the few things I've gotten into arguments about with people here, but I'm always happy to do it.