What this all demonstrates is that the Eurozone needs to become a full fiscal union. What is happening in Greece, with the effective seizure, or at least oversight, of the Greek government's fiscal powers, is what needs to happen.
Currencies like the US dollar work because, while there may be fifty states that use the USD, there is a single issuing central bank and a federal government that holds core constitutional fiscal powers. That's why you can have economies as diverse, small and large, as Rhode Island, Tennessee, California and New York in one federal state, because there is no "sharing" of fiscal sovereignty. The states are free to borrow money, but they have no control over central fiscal policy.
In other words, as so many have been saying since Maastricht was signed, for the Euro to actually work, the Eurozone needs to effectively become a single state, and EZ members need to surrender their fiscal powers to a central fiscal authority.