I ALWAYS put 2 spaces after a period. I was taught this was proper typing in high school. Now its habit, and I doubt I'll ever stop. In fact, I have corrected other people who don't do this...
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Continuing the hijack...
Okay, this is weird. I cannot believe I haven't noticed the double-spacing going on here before. I'm going to guess that the site updates a few days ago also included an update to the forum software that started rendering double-spaces (a double space in HTML is rendered as a single space unless one of the spaces is changed to a non-breaking space).
Regardless...
Brian, I can't believe you correct other people who don't double-space! There's nothing RIGHT about putting two spaces after a period. It was originally introduced in "style guides" as a "hack" when typewriters started to gain widespread use and promptly removed again once typewriters gained proportional fonts (the very first coming in the 40s, but general usage somewhat later). Typesetters with access to proportional fonts NEVER used the double-space.
Apparently, typing teachers stuck in the past, unable to get past what they themselves learned when they were young (and used mono-spaced typewriters), continued to teach this anachronism to their students. Sigh...