The early morning of January 1st, 2002: The switching.
There is only one way to describe the early hours of the currency switch: madness.
Since the largest distribution effort of Euros was conducted through automated teller machines (ATMs) and in New Years Eve its is common practice to party the night away the image of the night will be mildly intoxicated groups of people withdrawing the new bills as soon as the clock stroke 00:00:01.
January 1st is a bank holiday and only the Central Banks opened to receive the unexpectedly large crowds that wanted to exchange their savings into Euros.
This will turn out to be the only logistic glitch of the whole process. Monetary authorities underestimated the fashionable component of the "new thing in town" that drew more demand than initially expected. In the big scheme of things this was nothing more than an anecdote since the co-existence period between old and new currency was long enough and there was no shortage of currency at all.