There are also some questions, say economists, about the euro zone's rigid membership requirements. Countries must meet certain targets for inflation, budget deficits, and long-term interest rates, but no one is quite sure what will happen if a member violates the targets. Would Germany really be expelled for exceeding the budget deficit limit? And, if it did, could the euro survive without the strongest economy in Europe?

And that still doesn't take into account what could happen in the next decade when former communist countries like Poland, Hungary, and the Czech Republic - with their much less developed economies - are scheduled to join the euro.

"One of the things that has made the euro work is that the members have accepted the ideas of free movement of capital and goods and services across borders," says Achuthan. "Can that mindset be extended? It's a question that no one has an answer to yet. I'm not sure it's a question that a lot of people have started asking."
Until then, officials like Achuthan at companies across the U.S. and Europe will appreciate what has worked. It's a whole lot better than preparing 12 sets of financials.

Talk to any traveler who spends substantial time in Europe, and each, no matter how experienced and savvy, has the same story. They have local currency left over from the switch to the euro, and not only will businesses not accept it, they can't find anyone to change it to euros.

"I was pretty surprised the first time I walked into a shop in Belgium, and the owner wouldn't take my Belgian francs," says Joel Mokyr, an economic historian at Northwestern University in Evanston, Illinois. "I've got all these Belgian francs at home. What was I going to do with them?"