On-line stores from the Euro zone or the United Kingdom will be surely very happy with the newest option - capability of automatic currency exchange rates calculation on basis of rates offered by European Central Bank (ECB) and Bank of England.
If you set your default billing currency to EUR, all exchange rates will be automatically downloaded and calculated on basis of the European Central Bank rates. If you choose it to be GBP, rates will be downloaded from the Bank of England. Exchange rates are automatically downloaded every dozen of minutes, which greatly affects updates of prices displayed in other currencies.
More information about currency exchange rates and automatic rates calculation can be found on "Currency configuration" website.