Why You Should Never, Ever Use Two Spaces After a Period
Typography war on Slate!:
And yet people who use two spaces are everywhere, their ugly error crossing every social boundary of class, education, and taste.
What galls me about two-spacers isn't just their numbers. It's their certainty that they're right.
No subtle gradations here:
Type professionals can get amusingly—if justifiably—overworked about spaces. "Forget about tolerating differences of opinion: typographically speaking, typing two spaces before the start of a new sentence is absolutely, unequivocally wrong," Ilene Strizver, who runs a typographic consulting firm The Type Studio, once wrote. "When I see two spaces I shake my head and I go, Aye yay yay," she told me. "I talk about 'type crimes' often, and in terms of what you can do wrong, this one deserves life imprisonment. It's a pure sign of amateur typography."
I can't say that I recall noticing any unrepentant two-spacers in my history of correspondance. But I don't know whether that's because my circle of acquaintances don't do it or because it never occured to me to pay attention to it. Personally I guess I'm too slack to bother hitting the space bar more than once. I've never been tempted.