NKhp Twihard via Twifans was lucky enough to grab the earliest copy of the New Moon Movie Companion Book and she shares these tidbits. I only chose the most interesting ones. Read: Involving Edward and Bella. To read everything click on her site. Thanks!
While filming the breakup scene in the forest Rob and Kristen were being swarmed by mosquitos.
They scouted many locations for the Cullen house, but found one that "was comparable enough with the house in Portland."
The Cullen house used for Twilight was "a very specific house, and the only way out of that puzzle for us was to put portions of the story of New Moon in other parts of the house".
The sequence for the birthday partyl "Edward relates the history of the Volturi to Bella, she becomes wounded in the hand, and Edward faces off against Jasper."
Rob quote: "The birthday scene at the Cullen house is like the ideal birthday party. The house is beautifully decorated and everyone is happy. Edward is looking at Bella and thinking that she can become part of his family and his life--that maybe this can work out the way he wants it to."
They used full scale cutouts as a visual reference for the wolves. Each weighed 20-30 lbs and had a hole in the side for someone to use to carry them.
The wolves were each given characteristics based on the actors playing them, which is linked to the characters in the story. (Same=big and black) (Paul=more muscular and aggressive) (Embry=thinner and smaller)
It was important to make Jacob's wolf "iconic". In the animation he had to carry himself with an air of pride and nobility.
Wardrobe for the Cullens was updated. Chris Weitz felt that in Twilight they were a little too seperated color wise from the rest of the people in town. So they added a bit more to the color pallete, staying in the cool realm, but moving away from pastel hues to steel grays and blues.
Makeup was changed also to make them more translucent, without appearing stark white.
Edward's appartion was seen as a "flame" moving elegantly and fluidly. Chris gravitated toward this because it was like Edward was carrying a torch for Bella.
For 90% of the film Rob appears in the same suit he wore at Bella's birthday party.
There is an original flashback to the meadow scene with changed "sparkle effect"
The film makers wanted to make a fresh interpretation of the "diamond guy" effect, similar to sunlight on snow.
"We decided to something based on the sparkle of this statuary marble from Thasos, a Greek Island, which I always kind of thought the author was going for with this vampire effect. It has a kind of crystalline structure, this diamond sparkle. Another inspiration was the way Tiffany lights its diamonds, how the multifaceted surface sparkles when light hits it. From that starting point, we then wanted to enhance those qualities with a slight translucency."
Edward arrives in Italy wearing the SAME suit he's worn for months. The pristine suit is now threadbare, the jacket is gone, his pants are diry and his shoes are all scuffed up!
Bella's first view of the Volturi is in a painting at the Cullen's house. In a magical transition the camera pushes into the painting and takes us back to the past.
MAJOR SPOILER At one point Edward's head gets smashed on the marble floor and his vampire skin appears to crack, along with the floor. It seems Edward is done for, but his wound suddenly heals. Chris Weitz spoke with Stephenie and got her approval. Any ideas or questions always went through Stephenie since she has the whole mythology in her head.
Quote from Rob: "All the vampires, especially the Volturi, seem very comfortable with their existence, but they see themselves as monsters. And when they see this human who says, "I love this guy,' they all obviously want that, too. They want ot believe that can happen. So that curiousity, their fascination with that, is essentially what saves him."