Two spaces or one at the end of a sentence?

My buddy Michael asked the question, and pointed out that if you use two spaces at the end of a sentence, and you're writing HTML, then the web browser will treat it as a single space. But really, reformatting goes way beyond that. If you write something like the following:

The skies they were 
ashen 


and sober /          the leaves they 
were crispéd and 


sere. 

it will be rendered in HTML like this:

The skies they were ashen and sober / the leaves they were crispéd and sere.

To verify, select "view source" in your browser and search for "ashen"