I built a demo, for a rich text editor, for fastmail.fm. The editor is called Squire (http://neilj.github.io/Squire/) and designed for essays, emails, longforms ect. Squire uses contenteditable within an iframe. However, the editor replaces all the functionality of content editable to create a higher level of compatibility across browsers.

Thanks for your article, I really enjoyed it. Matt (http://www.matthewbordenweb.com/)