Each viewing of this movie becomes a little more enjoyable, I'd say. There are a number of "adult" issues in the film that I never understood as a child. The death of Trusty disturbed me the first time I saw it. I think it was one of the first times I ever saw someone die in a movie, dog or otherwise. Funny how I always think he dies each time I watch it. Spoiler: he doesn't die, and I'm always glad to see Trusty alive!
The "Making Of" documentary on the DVD is just as enjoyable as the film. It features: interviews with Disney experts explaining how the story originated in the 1930s with an idea from Disney animator Joe Grant; original TV footage with Walt Disney himself talking about the movie; Frank Thomas' son and wife enjoying home video footage of Frank studying dogs in the backyard; Ollie Johnson's thoughts about the film; footage and photos of Peggy Lee rehearsing and recording the songs, featuring Peggy Lee's daughter.