The Dubai government last week called for a standstill on the $50 billion-plus of debt at Dubai World, a government-owned investment vehicle -- a move that at least for a time rattled global markets. While Dubai World is widely seen as government-related, the emirate does not explicitly guarantee the vehicle's debts.

Fannie Mae and Freddie Mac, the two U.S. government-sponsored mortgage enterprises, were taken into conservatorship by the government last year after mortgage losses hit their capital. The Treasury provided capital lifelines of $200 billion for each of the companies, but still does not explicitly guarantee their more than $1.6 trillion of combined debt.