Lots of times I've seen movies that were of books I had previously read, but this is the first time I did it backwards (I think). I saw this on the ebookshelf the week before we left for vacation and I was looking for beach reads and thought, why not. Then, I didn't end up reading as much on my trip as I usually do and so came home with it still unread on my kindle. I debated with just returning it, but figured it was short and quick and so I'd just read through it this afternoon.
It was slightly different from the movie; in the book Sid plays a bigger role and is the catalyst for Julie discovering the affair. Typically one expects the movie to be not as good or to leave stuff out, but I was surprised to see that the book did not add much. Maybe it is because Clooney is such a good actor or that the movie was so well done, but I'm not convinced that in this case the book is actually better.
Overall it was a decent read, but I would recommend the movie as much and it is about 6 hours shorter.