I swear, the issue of double versus single spacing after periods came up for me a couple of years ago. I had a new editor, and she asked me to stop putting two spaces after periods. She never said,"Move into the computer age, you old hag," but since I hadn't even been aware that I was doing anything that could be considered incorrect, I did feel a bit twentieth century.
What a pain in the neck it was making the shift. I got over it, though, because I'm still young enough to be trainable.