Just to follow this up, the kindle service to convert the HTML seems to work well, and I have now grasped how the "free" service works.
Even if you have the 3g version of the Kindle, if you send it to the free email address for conversion it isn't delivered until you are connected to the Internet via a Wireless connection, and hence no charges are incurred.
Sorry, this has gone somewhat off topic. I did start off looking for Orgmode tips, but it drifted off.