I like -- for mdash and === for separator:
(setf org-export-html-special-string-regexps
`(
("^-----$" . "<hr/>") ;see also === below
("---\\([^-]\\|$\\)" . "—\\1")
("--\\([^-]\\|$\\)" . "—\\1")
("^===$" .
"<hr width=\"10%\";
style=\"width:10%;color:#000;background-color:#000;height:1px;border:none;\"
/>")
,@org-export-html-special-string-regexps))-- The Kafka Pandemic: http://thekafkapandemic.blogspot.com
