A nice cool breeze is only acceptable on a hot beach, not through the windows on a cold winter evening. Not to mention the money you are wasting by overheating your home to compensate for the drafts. For those leaky areas, install weatherstripping around doors and caulk cracks around windows. Schedule professional maintenance each season for heating and cooling systems to ensure all joints are connected and well sealed. Handy enough on your own? Use a mastic sealant or foil-backed tape to seal ducts. Aaaah, warmth.