Wow, the problem is that European Union is not working as a single economy, this organisation obviously ties those economies yet there are so many differences beetween nations states no once could consider EU as a single economy.
To name a few (cause its late):
-Euro is only a currency in 16 nation states
-There is a huge economic difference beetween states from Former Eastern Bloc (Poland , Hungary, Latvia) and those from the "old" Europe; France, UK or Germany
All those countries benefit differently from common agricultural policy for example
-There is a single market, but there is stiff competition within it.
Plus Europe will never become Unified like the United States, i think it is a bit naive to believe in it. Too many cultural, language, ethnic and historical differences have been beetween the countries, and still are. Plus i dont think that majority of us Europeans would like any more unified Europe (european parliament does not really exert much influence on Goverments, it has authority but rarely uses it). Constitution was rejected recently as well.
European Union is not doing as well as some people might think.