Hi. I registered only for this.
First: thank you SO much for doing this!
Sadly I tried using your plugin with the latest version of calibre and Kindle previewer 3 on my mac but i got an error message and the conversion failed.
here is the log:
http://pastebin.com/uUhqQWny
I'm not using any antivirus that could interfere.
It crashed with the Frankenstein book you linked. Later I tried to import the book in kindle previewer and got the "Enhanced Typesetting: Supported" message, so this seems to work.
Thank you again for your work!
Antonio