I was taught to double space when I took typing in junior high. Twenty years ago, I was informed that the standard was now to single space, so I changed how I did it. It never occurred to me to whine about it for two decades instead.

One thing I do now whenever I set a book up is fix the extra spaces. Not just the double spaces after periods, but places where the client has attempted to format the book by indenting paragraphs five spaces.