Here is a good point about Japan:
If there’s one asterisk to put after the shocking comparative figures, it’s that the debt-to-GDP ratios don’t take into account Japan’s huge asset holdings. At the end of March 2012, Japan’s central government had assets totaling some Y600 trillion, roughly half of its total liabilities projected for next March, separate MOF data show. And those assets include Y250 trillion in cash, securities and loans. Critics often say Japan’s fiscal health could quickly improve if the government sells some of those assets, a step the MOF is reluctant to take partly on worries that doing so could deprive lawmakers of incentives to improve government finances.