I noticed a few years ago that Americans often type two spaces after a "period". I've always thought it was a practice that should have died years ago; valid when all that was available was a typewriter's monospaced typeface, but horribly outdated as soon as proportional typefaces became available. A similar habit used to be common in Spain, where, in an upper case word or sentence, any accented letters were written in lower case, e.g. CAFé. Even when handwritten. Seemingly it had started with anglo-centric typewriters' lack of ability to move the acute accent upwards when typing in upper-case. This pragmatic—albeit ugly—solution somehow filtered into handwriting, becoming the "correct" way to write uppercase accented letters. Luckily it seems to have fallen out of use—I've not seen it in the last 5 years.
Back to the two space after a period issue. After "discovering" this habit I read up a little and was surprised to find there are still proponents of it. I chalked up my dislike of it to just being another pet peeve of mine; double spaces after a period don't really affect text, after all. Then the other day I noticed this:
Take a look at that third line. It looks horrendous and is going to be the irrefutable proof that typing two spaces after a period is evil which I will refer to forever more. In the meantime I'll get back to sperging over other typographic crimes.