The book is hilarious. That said, I will avoid this movie in the same way I avoid everything that Redford is involved in.
Redford? Blech!
He walked sections of the trail with an old friend of his, but did not attempt to walk the entire trail.
One through hiker who has walked the entire trail several times is J. R. Tate, whose trail name is Model T. His book about his first through-hike, Walking on the Happy Side of Misery, is excellent...one of those books it is hard to put down once you start reading. I haven't hiked the trail myself but I think Tate probably does a better job of conveying what the experience is like. He certainly has the credentials.