I wanted to be able to convert the Sony/Google epub books to Plucker, so I wrote a little perl script to do that.
http://pruss.mobi/epub2plucker.zip
You'll need a copy of the standard Plucker Desktop python-based parser, and you'll need to edit the first lines of the script to adjust where your python and plucker are, unless you're on Windows and have the default settings. You'll need the XML::Simple package for perl, and maybe some other packages.