I don't actually go to theaters very much, but I let friends talk me into going to see Marley & Me. I heard going in that it was one that required tissue, and that was spot on. It's a really cute movie that's really well done, but it'll definitely be difficult for anyone who has gone through having to put a pet down that you've loved for a long time. Still, it's a must-see for dog lovers. Maybe not in the theater, but definitely at home once it's on DVD. I do still pretty much detest Owen Wilson, but he's passable in this.
It will be particularly hard on those who have or had rambunctious Labrador Retrievers.