Would Europe and USA benefit from a single currency - for example "Euro Dollar"?

The main difficulty for any merged currency is the control needed from the Central Bank. One single central financial authority needs to maintain the value of the currency, match government spending and taxation income, control non-productive spending [which may include the military] and ensure probity in the financial sectors of all countries in the currency zone.

Now, is the Fed prepared to assume that responsibility for all the Eurozone economies? Greece, Spain, Italy, maybe Turkey in due course, Slovakia, Croatia? These are sometimes backward almost-feudal economies or else recent communist states.

Or, alternatively, are Americans prepared to let the German Bundesbank take control of the US$.?

I suggest the responsibility is too great. And the risk of it going wrong. It's easier for Central Banks to specialise and trade; as good-old-fashioned economic theory predicts.

The Euro can't even stand on its own. The only real economies in Europe are Netherlands and Germany.

No i dont think so, for one the euro is worth more than the dollar ( i think this answers the other guys question ).

I don't think so, I think it's a good idea to be able to compare the Euro to the American dollar to see which is worth more

no i dont think so becuase if the 'dollar euro' fails there isn't a strong currency to fall back on, plus canadian and austrialla and other countries would have to change aswell as they also use the dollar.