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).
"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
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. :)
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