Once you get older your body doesn't need milk. You can get great sources of calcium from other foods, such as vegetables.
The only reason I drink it is because it tastes good to me still, I enjoy a glass of milk in the morning, or a bowl of cereal. It's also a great source of protein, an excellent source of casein protein to be exact. If you weight train or do any fitness, you probably mix your shakes with milk, it's either that or water.
A good mixture also, for the weight trainers out there, 1 cup of milk, 1 scoop of vanilla whey, 1/2 cup of water, and one scoop of powdered gatorade/powerade (preferably orange). Mix it all together and add a few ice cubes, it's like a creamsicle. Good shit! You get your post-protein and your insulin spike all in one shot.