The euro will become the currency of more than 300 million people whose economies, taken together, are considerably larger than America's. But on a far less theoretical level, the euro is going to force huge changes in how both European and foreign businesses work. In the process, it may create some interesting opportunities for companies from across the Atlantic. Western Europe is indeed a common market, but it is far from a single economy. Prices for everything from cheese to cars vary widely.
Wages are far higher in northern Europe than in the south.
Tax structures differ greatly. Some firms, particularly smaller ones, are wary of buying and selling across borders lest they get blind-sided by shifting exchange rates. Monetary union will quickly change this. Big European companies, which will keep their books in euros, will increasingly treat the eurozone as a single market. Too bad for the thousands of smaller businesses that have thrived in obscure niches of their country's economy.