We agree with centaur, as we have posted many times previously our suggestions to purchase low for future use. Additionally, having a few Euros, or other currency in your pocket when alighting from your flight goes quite far in getting a taxi to your hotel or wherever you're going, or getting a snack when you alight from a flight, as opposed to first looking for an ATM to exchange your money, or exchanging some at the airport, where the commissions are not as favorable as you would like.
Since we travel to countries that use the Euro somewhat frequently, we generally keep a supply at home, buying low for future use, which essentially is what centaur recommends because the Euro is now relatively low. However, we believe, as do a number of what we would consider informed sources, in the WSJ and on Bloomberg seem to think the Euro will be around $1.15 by year's end, so we part company with centaur on rushing to buy now. Although, if you do have a trip upcoming in the immediate future, you can't go wrong with his advice to lay in some at the current rate, which is considerably lower than what it had been until recently.
We eschew using ATM's while on trips, even though we have both an ATM and credit card which levy no transaction or third-party fees on us, because at an ATM you pay the going rate, whatever that is. And we have found that on virtually every trip we've been on, the going rate has always been higher than what we paid for our Euros in advance, although now that might be advantageous, in a declining Euro enviromnent. Of course, the ATM offers convenience, but we have never though of it being a convenience if we were running low on money and had to stop whatever we were doing to find an ATM. And you do get to pay for that convenience, if the going rate is higher than what you could have paid if you purchased in advance. But to each his own.