Btw. There's an interesting problem with the Japanese debt - if you look at Japanese demographics the population is aging rapidly. This means that the pension funds that hold the debt will have to sell out because the money needs to be paid out. Who will they sell to? Every major institution in Japan is already stuffed to the gills with bonds, so there are two options: print money or sell to foreign investors. Printing money is balancimg on a knifes edge ( which is what the Bank of Japan is currently doing). Currently Japan pays an interest of less than 1%, and yet they spend 25% of their turnover just on interest payments. If you print money inflation and thus interest rises. When they reach 4% they will spend 100% of their income just paying interest on their loans. They can of course print more money and keep depreciating their currency, but history shows us that that doesn't end well. Alternatively they can try to sell bonds to foreigners, but somehow I doubt that there are any takers unless the interest rate goes up. As a comparison Greece pays around 8%.
I'm not saying that Japan will definitely go bankrupt, I'm just saying that there are some pretty big red flags, and maneuvering around them is going to be damn hard. Since there are equally hard problems elsewhere in the world economy (as I hinted at above) there's a real chance that something somewhere goes awfully wrong.