I don't know - I'm scared of it. With all the shipping options I tend to get confused. And frankly I think they always come up too high, and/or are a bother. That way it's a nice flat round sum.
I'm more worried about not accepting credit cards through paypal. From the little I know, if you upgrade your account to do that they take a certain % (how much?) out of every transaction, credit card or not - is it still like that?