One Space or Two?

Lately the battle of the spaces has been brought to my attention. Since high school, I have been a faithful member of the school of two spaces; I put two spaces between a period and the start of a new sentence. I have noticed that whenever I post on my discussion boards for class or create a new post on my blog, my writing is automatically altered so there is only one space instead of two. This automatic altering, I would guess, is the source of my troubles when I was attempting to incorporate ascii art into my blog post-- Blogger automatically undid the "art" part and slid my beautiful butterfly into oblivion.
So what's the deal? I did a little bit of research and discovered what this is all about. And it has to do with technology! Back in high school when I was using a mechanical typewriter (and printing presses were this way, too), the letters in the typeface were all the same width. Because there were so many resulting gaps within the text, a double space was used to aid the reader's eye in detecting the beginning of a new sentence. With the advent of modern technology, computers and such, the fonts we use today are proportional; an "o" and an "i" no longer take up the same amount of space. So the end of a sentence is easily recognized with only one space, and putting an extra space in there can create "rivers" in the text that can be unattractive and distracting. The MLA officially uses a single space after all punctuation marks, but they do say that there is nothing wrong with using two unless you are specifically asked not to. This is a useful thing for a librarian to know! I would imagine that grammar and format questions are not uncommon at a reference desk, especially an academic one.
Until further notice, I think I will stick with my current habit, especially since these things are sometimes automatically adjusted for me.