I've heard people in French markets buying vegetables in 'livres', which I thought were supposed to have gone out with Napoleon (they weigh out something approaching 500 grams).

There was a time when Ireland had pounds, shillings and pence (oh, and guineas, of course), but the value slipped so that an Irish pound was not worth the same as a British pound and the currency was no longer interchangeable. What is to stop the same thing happening with euros?