Re: HOW IT WORKS *
@Arnaut: Language barriers are more of a perceived issue for monoglottal Brits.
More of an issue for Brits, maybe, but still an issue. In the USA, an anglophone can consider work in any state without serious linguistic barriers. For a Greek to be similarly mobile in the EZ he'd need a working knowledge of over twenty languages, from at least four different language families. Some businesses may use English as a lingua franca (ha ha), but the vast number of jobs where this isn't possible means that there's a significant language barrier. Why do so many economic migrants end up in camps at Calais? It's more likely because they have enough English to hope to work here than because we have generous welfare provisions (despite what the Daily Mail says - you wouldn't cross a continent just to get slightly higher benefits).
Yes, there are cultural and educational barriers to job mobility in the USA, but these can be discounted because they're constant for all currency unions.