Per the WOJ, it doesnt' matter to him what the actor looks like, it is how well they can play the character.
I'm 50/50 between Jim and some of you that feel the actor should look as much like the character as possible.
However, here are some of my pet peeves regarding picking actors for my all-time favorite book series:
The "DO's"....
1. They DO need to be of the same gender as the character in the book.
2. They DO need to reflect their character's background, for example, if their character was born and raised in Chicago, then they should have a Chicago accent.
3. They DO need to portray the personality of the character somewhat close to how he/she was described in the books. Don't be one of those actors that doesn't even look at the books because they are so arrogant that they want to "put their own spin on the character". These are established characters, don't think you can just go ahead and completely re-create them just because YOU are an AC-tor!
The "DO NOT's"....
1. They do NOT need to be the same height as the character is described in the book
2. They do NOT need to have the same exact hair color, length of hair, or the same number of gray hairs!
3. They do NOT need to be of the same color skin as the character in the book.
That being said, the lead actors probably should resemble their characters as much as possible, but as you get into the supporting cast, you can pretty much just get actors that will play the character well, not worrying too much about appearance, unless it relates directly to the story line.