-, --, --- is, IIRC, how it is done in LaTex and would be exceedingly simple to do on a typewriter. That being said, to break up sentences I use " -- " because I think it looks nicer than "---". I'll go now ;)
LaTeX is a markup language though, not ASCII art. I can get behind two dashes as a substitute if no en dash is available, but three seems too much and looks like halfway to a horizontal line to me ;)
