"United States of Europe" - whats you opinion?

My knowledge of history showed me two contradictory tendencies that happen one after another.
Consolidation and disintegration.
There is time when smaller countries join together be it willingly or by conquest. Growing to certain point and prospering for a time. Roman Imperium, Austro-Hungary, USRR... You can check the rest. This are only examples.
And then it's point when this big things fall apart. Like the ones above in smaller or really small parts. Nationalist tendencies, unfair treatment of different regions. Reasons are different.

EU is modern analog of this things. Common (at least partially): laws, finances, economy...
It's a lot less rigid than the old ones examples but sometimes you can see moves that would want more solid unification and of course the opposition. Really difficult subject.