As the central banks are only purchasing the government bonds of their home countries, the member states will recoup much of the interest payable on these instruments at a later date via central bank profits. That can, of course, ingrain certain habits and ultimately encourage countries to put the necessary consolidation of their public finances on the back burner.
It began as a liquidity seizure in the financial markets when the credit boom came to an end after the subprime mortgage collapse, leaving US investment banks heavily strapped for cash. Then moved on to be more of a solvency crisis, when we began to see the rapid turnover of marquee names in the global financial stage. Then a confidence crisis.