I've lived on and fished Long Pond for over 25 years. Only during particularly severe winters does it freeze over completely. Most often you'll get a frozen shoreline and open center. Because of its east / west orientation, during the winter months it's frequently very windy so there's a lot of water movement. Rarely have I seen any ice fishing, it's just not very safe there.
Yeah, it's a real short season on the south shore. By the middle of Feb. the edges start to go. Plenty of ice remains out on the ponds, just real difficult to get on it!