The gyrations will hurt the good and the bad in ways that single currency per nation would not.

One way or another each nation in the EU is screwing another.

The EU currency is like a bunch of gay men each with a different std having unprotected sex.

The loved it, remembered it fondly, the swore up and down about getting screwed like that when their socks fall of and they need diapers for their dripping asses.

Wow this isnt a dig but after all the clashes I have had with Einstein it suprises me to agree with him!

In the UK there was a huge interest in joining the Euro and Gordon Brown (the then chancellor) refused to let the country do it.
He argued the first decade would really define the currency, that a recession could spell disaster and that a country on its own currency had a better chance to emerge from any economic crash much stronger.

As it is even those Euro Zone countries not badly affected by the recession are now suffering from the Greece bail out and it looks like spain is set to follow.

That said the US national debt stands at 13 trillion and just found the ratio of debt to GDP is worse then Spains

strong currency/ weak currency both have advantages and disadvantages:

strong currency:
easy to invest your money in weaker currencies: when euro was strong and dollar weak it was easy to invest 10k euro in american company as that translated to about 14600 dollar at some point
but this means that smart people invest the european euro's in american dollars, yen, etc, etc. meaning the money is leaving the european countries untill it balances out

weak currency:
this attracts investors to that currency. the dollar is stronger then the euro so americans investore now invest in european company's as it gives them more.
this means more capital comes in the eu-countries.

this being said. these are only textbookexamples. they don't consider the reason of the fluctuation. in this case: the bankrupcy of greec will scare of some investors despite the low euro value( and this is what einstein means I guess?)

about why a single currency like the pound can come out stronger then a common currency:

if the pound is low then everybody not using the pound will be attracted to investing in that country: aka: eurocountry's, america, asiancountries, etc.

if the euro is low: that means every country using the euro is in the same predicament. meaning that extra capital has to come from farther away through investments: america, asia, etc, etc.

and whilst it's way to early to be sure of a failing of the euro by this I can see some of teh points made here that have to be adressed by europe.