One of the more amusing pieces of fallout observed in early 2002 from the conversion of the European Union to the euro for real-world transactions was the discovery that many European vending machines were prone to confusing less-valuable coins from Thailand with the 2 euro coin.
The 10-baht coin has the same weight (8.5 grams) and very nearly the same dimensions as the 2 € piece (the baht is 0.25 mm thicker). Both coins are bi-metallic, with a gold-colored center and a silver-colored outer ring. The result was that many vending machines could not distinguish between the two coins. Bad news for vending machine operators- the 2 euro coin is worth 8 times as much as the 10 baht coin! More advanced vending machines- capable of judging metallic content- are able to tell the two apart, but many other machines required refitting (often only a software update), or had to be replaced.
The problem first appeared in Spain, but later spread as enterprising world travelers discovered that they could turn a nice profit by using left-over 10-baht coins in unsuspecting European vending machines. The problem was quickly resolved by vending machine operators eager not to loose money on underhanded currency conversions, and was expected to dissapear by the end of 2002.
(For reference, as of April 2002 1&euro = aprox. 38.5 baht, and 10 baht = 0.26&euro)