I just watched The Writer's Room on the Sundance channel with Benioff and Weiss. I have seen all episodes so far, and its really interesting.
The Writer's Room
George R.R. Martin quizzed them on who they thought was Jon Snow's real mother. If they had not answered correctly, they believe that Martin would not have let them do the show.
They also said that Martin had been approached by a couple of studios who wanted to turn the books into a movie franchise because the Lord of the Rings had been so successful. Martin turned them down because he did not believe that his books could be adapted into a 2-3 hour movie.
The show costs a little over $6 million per episode, making it the most expensive show on television. The pilot was so bad that it was reshot after HBO picked up the series. In the original pilot, George R.R. Martin had a cameo, but when it was reshot, it was removed.
The roles of Catelyn Stark and Daenerys Targaryen were recast after the pilot. The original actors were
Jennifer Ehle and
Tamzin Merchant respectively. There were also some minor parts recast as well.