Speaking of carbs, here's a tip for those who love mashed potatoes but don't love the carbs: Mix mashed potatoes with mashed turnips or cauliflower, about 50/50. Those veggies are lower on the glycemic index, and will actually make the 'tates more delicious. Add a little butter or olive oil, low-fat milk or sour cream, chives or garlic.
Leftovers? Form them into patties, coat them in breadcrumbs or the like, a little parmesan, and lightly sautee.