I do, just like they taught me in 10th grade typing class. But a quick sample of my incoming e-mail suggests I’m the only one, apart from Mrs. Q and my mom. Mrs. Q informs me the APA styleguide demands one space after a period: she uses the double space in e-mail but not in papers. LaTeX splits the difference, using an intersentence space about half again as large as the space between words. The iPhone automatically drops in a period when you double-space after a word, which seems designed to suit habitual double-spacers like me; on the other hand, the text it actually produces has just one post-period space.
So I’m confused — has this tradition really fallen out of use and no one told me? Or was it never a tradition at all, outside my high-school typing class?