I just came across a nice page which summarizes the use of the proper HTML character entities for common punctuation. I know this has been discussed before, but this page is a nice summary.
http://csswizardry.com/toybox/punctuation-glyphs/
The one point of the chart I questioned is the use of the hair space around an em-dash. According to Wikipedia, it is not commonly used (at least in the US).
http://en.wikipedia.org/wiki/Space_%..._around_dashes