What do you think of American actors' British accents?

Gwyneth Paltrow was amazingly good with her accent, both in Shakespeare and Sliding Doors - I wouldn't believe she wasn't English. Ditto Nicole Kidman in The Others. Johnny Depp, often cited as "the best actor in the world", was worse than Dick Van Dyke in From Hell. Utterly appalling, in fact. Hugh Laurie is perfect in House, from what I can hear, not being native to America myself, though Americans have said the same. Brad Pitt did a wonderful Irish gypsy accent in Snatch.