I found The Curious Case of Benjamin Button: Story to Screenplay in my local bookstore last week. I've finished Fitzgerald's original story, and I doubt I will read the screenplay.
Fitzgerald's story was okay. It was definitely shorter than the movie. This is one of those rare cases where I think the movie is better than the book. There are a lot of things that were changed for the movie, but it would be almost impossible not to change a lot when adapting a short story.
I've also just finished reading Confessions of a Shopaholic (Movie Tie-in Edition) by Sophie Kinsella. The book was okay. I found Rebecca Bloomwood annoying at times. I'll probably read the other books out of curiosity if I find them at McKay's, the best used bookstore in the world.
I've seen the previews for the movie several times now. Judging from the previews, I don't think the movie will be very true to the book. But that might not be a bad thing.