I tend to use two spaces after the period. At one point I did only use one space but I went back to old habits.
I think it's easier to type one space after the period and you have less rules to remember. I'm quite interested to learn that this is a leftover from typewriters though, simply because I find it quite an interesting fact.
Personally I really don't mind if I use single or double spacing but I pretend to myself (like I did when I was tiny and first learned this) that I'm more professional and grown-up. I figure this is just one of those "development" things that happen. English is an ever-changing language and this is probably going to be one of them. In a generation or two it'll be all one spacing after the period.
It's like the speech marks thing. In writing I was taught to do them in the shape of 66 and 99, but now I write them more like //. In typing most people show speech through 'single marks like these' whereas it used to be "double marks like these". Anyone who RPs regularly with me may have noticed a switch in speech marks by me - back to old habits yet again. There's something quaint in being old school that attracts me.
Plus I always wanted a typewriter. I think I'll invest in one when I grow up and go clickaty-clack on them. I'll probably waste a whole bunch of paper from making mistakes and not backspacing, or being able to. I ought to practice better typing more - I rely on the backspace too much.
What are monospace fonts, vermilion?