One space after a period, known as a "full stop" in England, I hear. Why would you need a moat after a stop sign. It's overkill. Here's a good test for you two-spacers. Squint your eyes and look at a paragraph typed with two spaces after each period (it should look blurry, leaving you look at soft shapes of gray and white). Full of holes. Keep your eyes squinted and check out a properly-spaced paragraph with just one space after each period. It's just a nice mass of gray. You want the reader to move beyond a period, to know when a sentence stops, but not to stop the flow of your reading. You already have a full stop, not to mention what amounts to an extra space above the little dot. Anything more is a waste of a click and a disservice to your readers.