This concept isn’t new, it’s just becoming more easily available. It’s like a prepaid credit card, and the idea is that if it gets lost or stolen there’s only so much credit that can be stolen. It’s not linked to any of your usual bank or credit cards. It could also be considered a disposable credit card. (And the term debit would be more accurate than credit).
In Australia there’s now a new credit card that works in this way called V-Card. It carries the Visa logo and can be used just like any other Visa credit card, only that you can put any value you want into it before you start spending.
Since the whole idea is to avoid online fraud you probably wouldn’t want to buy one online. They’re going to be available at real shops (Mobil/Quix for now), you then activate it online and they send you the security details by email or SMS to make you feel more secure. There’s a $5.50 setup fee on top of the credit.
It’s a good idea for many people, especially those who have avoided online shopping till now. It could also be useful when travelling overseas (so many travellers return with stories of how their credit card details were stolen).