Posted: Wed Mar 21, 2007 10:30 pm
You are hereby found guilty of not having read the thread. HTML swallows multiple whitespace. 
Traditionalists say two. Computers say one. LaTeX renders two.
So: When writing or using a typewriter, two.
On a computer: One. If you're using LaTeX, it's two and you don't have a choice anyway - it'll convert for you.