Readers of this blog may know that there is a fiery debate out there in the grammar world about whether you should have one or two spaces after sentence ending punctuation. This seems to be, in part, a generational issue. My experience is that those who were born in the 1970s or earlier tend to use two spaces, since they learned to type on typewriters (typesetting standards led to that convention). People born in the 1980s or later are a mixed bag, but are often taught to use only a single space, since computers do proportional typesetting which no longer requires the extra space.
As with many grammar debates (such as the debate over the ghastly practice of pairing a plural pronoun with a single noun), the proper approach is to pick a side and then fight to the death for it. For the record, I am decidedly on the side of two spaces. But this is increasingly a minority view. While style guides are mixed on the question (Chicago requires one space, Modern Language encourages one but allows two, whereas the APA style guide actually changed back to the two space convention in their 6th edition though they defer to publisher standards for final manuscripts), overall publication practices favor one space.
But I think they are wrong. A sentence end is a full stop, and the reader should be alerted to this by having an extra pause (space). My experience as a reader is that this make the text more readable. And Two Spacers can rejoice, since Science appears to be on our side. Specifically, a recent study looking at the “psychophysics” of reading suggests that readers read faster and with better comprehension when sentences end with two spaces. Read about it here.