of course the 28 degrees also earns money from the fact its a credit card and merchants pay. I've heard its a good card, but it has negatives like every other card!
I've found the cards in a foreign currency work quite well, because you can say put a few thousand euros/US/etc on it. The fees are in that currency, there is no more exchange conversions either. BUT it really depends on where you are going and I don't tend to visit just the USA and Europe.
please read this thread:
http://www.lonelyplanet.com/thorntree/thread.jspa?threadID=2295627
What about pre-paid cards? Caveat emptor. I see no benefit in using these. You load a card with Euros, before you depart. That means you lock in the exchange rate. More on that below.
Pre-paid cards often use a rate that is less advantageous than ATM withdrawals with a debit card. So you are losing money right there. And they often come with a host of (hidden) fees: top-up fees, administrative fees, and if you have less than €50 left you may not be able to withdraw it… so again, typically pre-paid cards are more expensive. They are often being flogged by banks to inexperienced first-time travellers- no experienced traveller I know uses them.