Don't Space Out; Space In

Which do you think is correct: one space or two spaces after a period?

-Spaced Out in NYC

Dear S.O.,
In the olden days when we punched out copy on a typewriter, and computers were the domain of mad scientists in grade-B movies, we were taught to double space after each sentence. But, when word processors became the natural mode of written communication, the way the gods intended it to be, we no longer had to double space. In fact, the double space between sentences is distracting, especially when text is justified. Arrrrgh. In sum, it's a style choice, like the serial comma or split infinitive. The best rule of thumb: if it's distracting, don't use it.
Thanks for the question. Good one.