The American adaptation, which will be directed by David Fincher and written by Oscar-winner Steven Zaillian (Gangs of New York, Schindler's List, American Gangster), doesn't have its leads set in stone yet, although it looks like Carey Mulligan is most likely going to end up as Salander. (Noomi Rapace, who plays Salander in the original movies, has made it clear she has no interest in reprising her role for US audiences.) Anne Thompson reports that Brad Pitt will be reading for the male lead, Mikael "Kalle" Blomkvist, in June.
The problem with Pitt is he's too good-looking and all-American. He's a fine actor and an excellent collaborator with Fincher, but Blomkvist is not a pretty boy. Although at least two of Blomkvist's love affairs were cut out of the original movie for the sake of time and streamlining what was already an unwieldy plot, he's not written as your typical lady killer. (There is a full-length mini-series version of Dragon Tattoo made for Swedish TV that includes these subplots, although when it's not clear if it will be released on DVD for US audiences.) One might, if one wanted to be ungenerous, say that it was a bit of wish fulfillment to make Kalle's character as attractive to women as he seems to be.
Michael Nyqvist, who plays Blomkvist in the original, is not hard on the eyes, but he's not the same type of handsome that Pitt is. He's good-looking in a normal way -- easy-going, a little pock-marked, and generally a decent enough guy that a woman could safely fall into bed (or in love) with. That's part of Blomkvist's appeal and part of what makes the extremely self-protective Salander allow him into her world.
Thompson suggests a few possible alternate leads, with number one being Mads Mikkelsen. I could definitely see that, especially since Mikkelsen is himself Scandinavian. Frankly, I can't imagine a more inappropriate, though typically Hollywood, casting choice than Brad Pitt. If Fincher and Zaillian plan to keep their movie close to the book itself, why cast one of the most famous and handsome men in the world to play an everyday journalist? Could he even play someone who's Swedish? Could we ever forget for a second that Blomkvist is Pitt and vice versa?