I'm usually late to the party for things like this so bear with me here. I'm just gonna leap into the fray of bajillions of other people who have already discussed this to death.
When I went to see this movie, I haddn't read the book. That may be #1 of nerd sins but give me a break, my "Want To Read" list is 400+ books deep. My opinion of the movie wasn't colored by the book and I STILL thought it was funny for all the wrong reasons. The scenes that should have been tense came off slow and there are so many holes in the plot, it couldn't protect you from a horde of zombies any better than a NERF gun. The movie's only saving grace was the visuals of waves of zombies rolling over one another like fire ants.
After reading the book, I am extra pissed at the movie. Max Books did a fantastic job of writing harrowing accounts from a wide range of perspectives (scientists, politicians, regular people, and feral children) in a gripping and at times heart-breaking story of the fallout of the zombie wars. There were parts where I cried because I was truly touched or horrified.
In comparison, there were parts of the movie where I cried... From laughter.
So, now that I have seen what has been done to the original source material, I would LOVE to put forth this challenge to the entertainment industry: Make a version true to the book in the vein (no pun intended here) of Interview with the Vampire or Forrest Gump. The real-time interviews interspersed with flashbacks is a formula that obviously works. Get to it, Hollywood! You know it would be awesome.