Come to find out, the "two space" theory has changed. Maybe I'm naieve but I didn't know something like that could change. Who decides when it does? I guess, they add new words to the dictionary all the time (not sure who decides that either) so why not change grammar?
Anyway, thought you might find it interesting as well.
The following was taken from the Grammar Girl website.
Now here's our first listener question.
Yes, the caller is correct and he's also right that a lot of people haven't heard about the change.
Two Spaces After a Period -- The Old Way
Here's the deal: Most typewriter fonts are what are called monospaced fonts. That means every character takes up the same amount of space. An "i" takes up as much space as an "m," for example. When using a monospaced font, where everything is the same width, it makes sense to type two spaces after a period at the end of a sentence to create a visual break. For that reason, people who learned to type on a typewriter were taught to put two spaces after a period at the end of a sentence.
One Space After a Period - The New Way
But when you're typing on a computer, most fonts are proportional fonts, which means that characters are different widths. An "i" is more narrow than an "m," for example, and putting extra space between sentences doesn't do anything to improve readability.
Notice how in this example, the "i's" and "t" take up much less space in the proportional font than they do in the monospaced font.
Although how many spaces you use is ultimately a style choice, using one space is by far the most widely accepted and logical style. The Chicago Manual of Style (1), the AP Stylebook (2), and the Modern Language Association (3) all recommend using one space after a period at the end of a sentence. Furthermore, page designers have written in begging me to encourage people to use one space because if you send them a document with two spaces after the periods, they have to go in and take all the extra spaces out.
I know it's a hard habit to break if you were trained to use two spaces, but if you can, give one space a try.
There you have it, your grammar lesson for the day, whether you wanted it or not!