Here’s an argument that everyone has something to say about: How many spaces are you supposed to put after a period? The answer is one. Putting two spaces between sentences, as many people learned to do in school — and are still learning — thanks to early monospaced typewriters “is totally, completely, utterly, and inarguably wrong,” according to Slate’s technology columnist, Farhad Manjoo — and every major style guide.
http://www.theatlantic.com/technology/archive/2011/01/why-you-should-never-ever-use-two-spaces-between-sentences/69579/