I've been testing htmldoc for my ebook conversion needs for the Sony Reader. Most books I convert are from
Gutenberg which these days tend to use a lot of CSS (and nice pretty pictures

), unfortunately htmldoc has limited support in the latest v1.9 for CSS - unless I haven't configured it properly. They still convert well but much of the formatting like centring is missing.
Apart from that it works great on all other HTML content and text based Gutenberg ebooks convert great after processed through
GutenMark
I can't find v1.9 binaries so compiled it using Cygwin.