To keep with the 'spirit' of what Gkirk has mentioned, Euro in the USA would be a bad idea, for the following reasons.
1) It would have to be renamed from the Euro -- because of the inclusion of France, it will have to be called the Freedom dollar or Liberty dollar or the We-hate-the-French Dollar (the last one could also go for the current Euro also)
2) The localised US Euro would have to have a value above the European Euro, just to remind the European Euro users of how the US Euro users saved your butts in world war II
3) It could cause a rift between certain states. SoCal, upon learning of the introduction of the Euro would demand to instead introduce the Mexican peso. Brooklyn would join the Russian rouble zone. Detroit would then start using the Saudi Arabia Riyal -- the blacks in Detroit who are unhappy with this, would then move to South Carolina, where they themselves would be introduced by white landowners as the unit of currency.
But then if it was introduced, the Europeans who were pissed at attempts by certain sections of America trying to rename the currency, and have control over it, could decree that the design of the notes would feature
€500 -- A380
€200 -- A340
€100 -- A330
€50 -- A320
€20 -- A310
€10 -- A300
€5 -- A400M