Depp's take on the Hatter is that he has mercury poisoning. Mercury was used in the felting process and hat makers breathed in the fumes which sometimes caused neurological damage. Hence the term 'mad as a hatter'. So it seems he's playing the hatter a bit differently than say, the Disney version. Whether it's more true to Carroll's version we'll have to see. But it's a Burton-esque looking film, and I'm expecting it to be a bit on the creepy side.