When people say that it is not right that the book (The Hobbit) has been extended to three movies, I feel that they just do not understand what Peter Jackson and co. are doing. He is not merely interpreting from book to screen he is taking source material from other places and combining it to create a more rounded narrative with as much middle earth lore as he can possibly manage. As a huge Tolkien fanatic this is a real treat. The whole opening sequence of DoS is taken straight out of Unfinished Tales, not The Hobbit, which is great as it adds more to an already amazing narrative.
While I understand that to the average movie goer, this seems insignificant, I feel that it is important for them to understand where Peter Jackson is coming from. To them (average movie goer), a movie should have the basic structure of a beginning, middle and end with the occasional sub plot thrown into the mix but when dealing with The Hobbit, in fact any middle earth tale, it is just not that simple. Tolkien created a very deep and complex world. One that requires many interwoven plot lines and extended explanations. It is not possible to just have a simple movie explaining the adventures of Bilbo and the dwarves to the lonely mountains. It is about including all the lore of middle earth that can possibly be included as this may be our final trip to middle earth on the silver screen and we want every bit of it that we can get.