Heya Katherine and Jeff,
It's fun watching you two have conversations sometimes.
I've just been waiting for someone to bring up the glamour-factor in the book vs. film difference.
I think it's definitely clear that the filmmakers made a conscious decision to make both characters more appealing (physically in terms of casting, but also in terms of mannerisms, etc.). I think this is particularly true of Jack. I don't remember where the interview is, but I recall reading Proulx talk about how she really likes Jake's depiction of Jack but that she sees the film character as really quite significantly different. I remember she thought of film-Jack as being like "quicksilver." I don't quite know what that means, but I like it.
I think that through casting Jake the filmmakers definitely wanted to make Jack more conventionally attractive, but I'm glad they conveyed some of his "average-ness" through keeping his awkwardness (it's interesting how Jake makes this "awkwardness" simultaneously endearing and charming) as part of his character. I like in the DVD special feature how Jake describes his understanding of Jack as a person who's "really trying" that the act of "trying" hard is just part of Jack.
Personally, I'm glad I saw the movie before I read the story. One thing I find strange when I read the story even now is that I don't at all feel the same level of emotional connection with the written characters. I love Annie's writing and phrasing, etc. But, I've never felt as connected to story-Ennis or Jack.