What can I say - I am no economist. Just thinking about behavior with this one: governments in Europe have taken action to guarantee deposits. Big deal? Yes: the deposit amounts are unlimited. Now, suppose you are the CFO of a significant corporation. Given the ease of money transfers in this age, wouldn't you be tempted to withdraw your money from a US institution not guaranteeing your deposits to place them in a country that is guaranteeing them? I think yes; consequently, I think it more likely than not we will see either one of two things (or both): a "silent" bank run and/or the US government guaranteeing every bank deposit regardless of size.
Now THAT is a scary thought.