One drawback is that it doesn't follow the standard $MANPATH directory structure (man/manX/Y.X where X is the section number and Y is the manual page) but instead uses a single flattened directory (man/Y.X).
Thanks for clarifying. Defensive instincts engage when one's pet project fades from the spotlight on its own stage. You're right about Pandoc fulfilling my quoted aspect of Unix philosophy; I realized it later but was too proud to admit it. :)
"when you don't create things, you become defined by your tastes rather than ability. your tastes only narrow & exclude people. so create." --Why The Lucky Stiff
Ronn's HTML output is indeed pretty, but I cannot say the same of its input. In particular, I find md2man's syntax for tagged paragraphs (all lines indented by +2 spaces except the first line) to be less intrusive and easier to maintain than Ronn's (list items that begin with boldface and end with a colon, followed by +2 space indented lines).
I filed an issue about this here: https://github.com/defunkt/gem-man/issues/8