One space, please
Space Invaders: Why you should never, ever use two spaces after a period, in Slate.
"Every modern typographer agrees on the one-space rule," says the column. "Every major style guide--including the Modern Language Association Style Manual and the Chicago Manual of Style--prescribes a single space after a period."
I've taken Farhad to task before, but I'm behind him here (even though I dislike how he positions his argument). I forcefully converted my own two-space habits sometime in 2004. It's ungainly, and it doesn't even render in HTML, where I spend much of my days. I've taken to performing a find-and-replace on any documents I have to proofread.
In fact, I can trace my period shifting to my first full-time position that required I use Outlook on Windows for email. Faced with seas of Arial, I could suddenly see how disjointed my text looked, after 15 years of Mishawaka in Eudora.
Habits are nice and conventions are nice. But clean, efficient typing is even nicer.