I was initially skeptical of a two-part split, but the proposed dividing line made a lot of sense. The book is actually packed full of many scenes, so I understood that those take a longer time to play out on the screen. Some appendix material explaining Gandalf's absence makes a lot of sense too and would be fun to see (once they got Christopher Lee, I figured it could be exciting).
Three concerns me because the split might be less logical and because the appendix material might start to overshadow Bilbo. I'm cautiously optimistic, but you have to recognize that the side story never overlaps with the main story. As much as he wants to tie it in with the Lord of the Rings, it also needs to stand as its own story. So my position right now is to wait and see what direction this takes.