Greece's 2 year debt is now at 33% interest. Ireland is at 23%. Portugal is above 19%. I'm not an economist by nature and I don't know how these nations defaulting would play out, but I am fairly certain that if they go under, Spain and Italy will feel the heat as well. If they default as well, the Euro is effectively finished.
None of this will be good for the world economy. The United States is hanging on by its fingernails to stay at the fairly miserable level we're at. Even if we have a deal on our own debt ceiling shortly, a hurricane like this from overseas might push us over the edge anyway.
The question isn't if this is going to happen, but when.