Buy money in US.

Yes, you most certainly have to worry about the exchange rate they will give you. Keep in mind that currency exchanges are a for-profit business that only does currency exchange. So they have to pay the bills and make a profit somehow. Either they charge you a high fee, a poor rate, or both. It is the most expensive way to get foreign currency.

It you have an ATM or debit card, you'll find it works just fine around the world (be sure to notify your bank of your travel plans). And even if they charge some fees, it rarely totals more than 4%. By comparison, you'll pay at least 10% or more at a currency exchange.

"Do I need to worry about their exchange rate being out of line?"

Yes.

There's nothing wrong with buying $50-$100 worth of foreign currency for your first country, so that you'll have it right away when you land. But there's no need to bring more than that. And unless you have an unusual situation, there's no need to buy both EUR and GBP before you leave the US. You can convert your leftovers when you're there. For instance, if you're going to London and then to Rome, bring some GBP from the US, but when you leave London or arrive in Rome, change any leftover pounds to euros.

Currently XE http://www.xe.com/ is showing the exchange rate for the US dollar as $1 = £0.588 = €0.743. Or, £1 = $1.698 and €1 = $1.346. Now you won't get quite those rates when you use your credit card in Europe for purchases, or when you use your debit card at a European ATM, but it will be close. So, knowing that, you can see how good a deal the airport is really offering. Realize the transaction fee is rarely where they make their big profit; it's the exchange rate difference. If you look at the spread between their "We Buy At" and the "We Sell At" rates, you'll see what I mean.

For just about everything you need to know about money in Europe, here's Rick's page of links. Read all the linked pages, and you'll be an expert: http://www.ricksteves.com/travel-tips/money

EDIT: You will see that three of us all posted the same advice within 5 minutes. That should tell you something [g].

Look at the bid-ask spread. The bid rate applies to selling and the ask rate applies when you buy. See: http://www.oanda.com/currency/converter/

The Oanda website notes that Interbank +/- 5% is the typical kiosk rate. Sell 1 USD gets you 0.70551€ at todays average rate. Buy 1 USD at today's rate cost 0.78180 €. The 0.07629€ difference is the spread.

The exchange rate may be in line with the Interbank rate but you will pay for the service one way or another. Note that different banks have their own transaction fee rates. A 1 or 2% transaction fee is common but your own financial institution should disclose that information. And while many will tell you that European banks do not charge ATM fees, I have had 1 or 2€ fees show up as a separate debit on my credit union statement attributed to the foreign bank. And the sky's the limit on private ATMs.

Don't be naive. Of course, they can be generous and wave "the fee" since they will soak you about 10 to 12% on the exchange rate if not more.

THX for all the replies JIM I ordinarily don't think I'm too naive, but was here.