Health-wise the skin is actually the most important part of the potato. The Skin contains half of the fibre in a potato, but is the smaller of the two parts. Being so full of fibre makes it perfect for people on diets because it makes you feel fuller for longer (It prevents slumps in blood sugars and a slump in blood sugars is the main reason people feel an urge to snack on sugary foods) Fibre also helps reduce the risk of colon cancer, heart disease and type 2 diabete. It also helps prevent constipation :D
Potato skin is high in the essential mineral Potassium, which lowers the risk of dying from a heart attack. Scientists have shown that Potassium from potato skin also reduces the risk of stroke, but that Potassium in vitamin supplements do not help reduce the risk of stroke.
Potato skins contain very high levels of vitamin C, almost as much vitamin C as an orange or other citrus fruits. Potato skins also contain B vitamins and are a good source of Calcium.
Some important things to avoid in a healthy diet are fat, cholesterol and sodium. Potato skins do not contain any of these main 'nasties'