And for Italian and Spanish banks, in today's febrile climate there is a strong temptation to put any spare cash on deposit with central banks, even for a guaranteed loss on that money, because they don't want to double up on lending to households and businesses struggling to repay what they owe, and they don't want to be short of cash if capital flight intensifies.

BBC: Can Draghi do 'whatever it takes' to save euro?

Under the new agreement, average savers' deposits with all Cypriot banks of up to 100, 000 euros will be guaranteed by the state in accordance with the EU's deposit insurance guarantee, the diplomat said.

NPR: Cyprus Secures Bailout, Avoids Bankruptcy

I'd been deep in the detail of deposit guarantees for a week already, after the Irish state guaranteed everybody's holdings to 100%.

BBC: Tick, tock: The risks of depositor flight in Greece

If a country seemed likely to leave the euro but its deposits were guaranteed in euros, people might be tempted to borrow heavily in their local market and deposit the proceeds in their bank.

ECONOMIST: The euro crisis

Montana and Arizona offer certificates of deposit paying 2% less than the increase in private college tuition, with a guaranteed minimum of 2% a year.

FORBES: Money & Investing