I was going to write something on why Farhad Manjoo's polemic on the double space after a period is dead wrong. But Tom Lee's piece on the topic is so superlatively better than what I would have written that I will just turn the mike over to him:
I'll take Manjoo's word that all typographers like a single space between sentences. I'm actually pretty sympathetic to arguments from authority, being the big-state-loving paternalist that I am. But, with apologies to friends and colleagues of mine who care passionately about this stuff, I lost my patience with the typographically-obsessed community when they started trying to get me to pay attention to which sans-serif fonts were being used anachronistically on Mad Men.
I love you guys, but you're crazy. On questions of aesthetic preference there's no particular reason that normal people should listen to a bunch of geeky obsessives who spend orders of magnitude more time on these issues than average. It's like how you probably shouldn't listen to me when I tell you not to use .doc files or that you might want to consider a digital audio player with Ogg Vorbis support. I strongly believe those things, but even I know they're pointless and arbitrary for everyone who doesn't consider "Save As..." an opportunity for political action.
Nor should we assume that just because typographers believe earnestly in the single space that their belief is held entirely in good faith. They're drunk on the awesome power of their proportional fonts, and sure of the cosmic import of the minuscule kerning decisions that it is their lonely duty to make. Of course they don't want lowly typists exercising opinions about letter spacing. Those people aren't qualified to have opinions!
(For what it's worth, I don't think you rabble should be using Flash or Silverlight or anything other than plain text in your emails. You can't be trusted with it! And, not that this motivates me or typographers at all of course (we just want what's best for you), but when you do such things it makes my job slightly harder.)
Manjoo's argument about beauty, like all such arguments, is easy enough to dismiss: I disagree. I find it easier to read paragraphs that are composed of sentences separated by two spaces. Perhaps this is because I, like most technologists, spend most of my time working with (quite lovely!) fixed-width fonts for practical reasons. But there's also a deeper beauty to the two space rule -- a sort of mathematical beauty. Let me explain.
Consider the typical structure of writing. Letters are assembled into words, which turn into phrases, which are arranged into sentences -- at the same time being assigned to speakers, a neat trick -- which are then combined into paragraphs.
It's a chemical process, a perfect and infinitely flexible hierarchical system that should command our admiration. Being able to rationally examine, disassemble and interrogate the final product is a mark of the system's beauty. Anything less is settling for a sort of holistic mysticism.
It's disrespectful to let writing's constituent elements bleed into one another through imprecise demarcations. If you see me "making mistakes with comma placement", please rest assured that it's deliberate. In most cases the comma doesn't belong to the phrase delimited by the quotation marks that enclose it. Placing an exclamation point or question mark to the left or right of a close-quote is a weighty decision! That we violate the atomic purity of quotations with injected commas is an outrage.
Let me just add: if you're spending time worrying over whether my emails contain one or two spaces, you need to ask them to let you out of the asylum more often so you can pursue a more interesting hobby. I double space after sentences because I learned to type on a manual typewriter, and it's not worth the effort to retrain myself. Even if typographers groan every time they open one of my missives.