British/American Accents.

We British often pour scorn on American actors trying to use a British accent. Dick van Dyke should have been taken outside and shot for what he did in “Mary Poppins”. Renee Zellwegger was brilliant in the Bridget Jones films, but IMHO that’s the exception that proves the rule. So I was just wondering what do Americans think of British actors using an American accent, for example the gorgeous Anna Friel in “Pushing Daisies”?