The really troublesome country is Switzerland. Firstly because it doesn't have a European Union backstop. Secondly because so many of the bank loans are to Eastern Europe and even worse are denominated in Swiss francs. Imagine getting your salary in a depreciating currency like the Hungarian forint and having to pay your mortgage to UBS in francs which have appreciated 40%. You'd be looking foreclosure square in the eye.
From The Atlantic's story "What Does It Look Like to Leave the Euro?":
The Economist has an excellent piece this week outlining just how difficult it would be to leave the euro. Bank runs, capital controls, angry voters, and where, exactly do you get currency for people to use?...
...Bank assets as a percentage of GDP...MORE
Luxembourg 2,461(For comparison, total banking assets in the U.S. are equal to approximately 82 percent of GDP.)
United Kingdom 389