I refer you to Brotherton Lad's textbook answer above... though as OHW says, it is imperative that butter stocks be closely monitored and transferred from fridge to dish in a manner so as not to leave no spreadable butter in the dish for impromptu sandwiches and the like. This would be a BAD SITUATION.
As to what happens in the winter if your kitchen is colder than a fridge, throwing the above butter management strategy off a bit, I recommend the airing cupboard or perhaps under one's pillow.