According to Farhad Manjoo of Slate magazine, it is wrong to put two spaces after a period.
While I am certainly not an expert in design or typography, I did take a keyboarding class in grade nine. I paid a great deal of attention in keyboarding class. I worked hard. I practiced. And I earned a perfect grade.
One of the things I learned in that class was to hit the spacebar twice after each period. As a result, for the last twenty years I have been typing at high speed and putting in two spaces after every period.
Manjoo makes a compelling argument that I have been doing it wrong. So from this point forward — or, more correctly, from the commencement of this post — we will attempt to do it right. That said, twenty years of typing makes for a well-ingrained habit to break.
Expect us to fail often.