I just got home to find the book Prometheus: The Art Of The Film waiting for me from Amazon. This is a really nice book and I'm looking forward to reading it. Maybe I'll also get some clues regarding some of the thinking that went into the film.
Yeah I flipped through the book and it seemed pretty cool. They talked about how the Engineers were originally going to be upsized to their proper height in post (as they appeared in Alien), but Ridley felt they already looked large enough as is.
The movie is also featured in the new Cinefex (along with Avengers). Looks like there's probably some interesting info in there too, but I haven't had a chance to read it all yet.