Andrew is right. Sweden, Denmark and the United Kingdom decided not to join the Euro when it was first launched. This is the list of EU countries using it : Belgium, Germany, Greece, Spain, France, Ireland, Italy, Luxembourg, the Netherlands, Austria, Portugal and Finland

More info in http://europa.eu.int/euro/entry.html

But during our last vacation we found out that many places in Slovenia were accepting Euros. The exchange rate was a bit worse than in a bank (but only a little bit), and in some places we would get slovenian tolars in return, but it was certainly very handy :) The motorway tolls had a display where they stated how much they would charge in Euros.

But coming back to the original question, if it is not very difficult, I have always liked to travel with some money in the currency of the country I am visiting. Not a lot of money, mind you, maybe 100 or 150 Euros just in case the ATM´s don´t work or the queue at the exchange booth is way too long.

Kind regards,

Covadonga Bilbao - Spain