sort of hijacking this thread with a quick note: In order to remove numbering from the headings produced by org-odt, simply export a file, go to Tools -> Outline Numbering in libreoffice/openoffice, and turn numbering off for levels 1-10 (probalby you only need about 4 levels anyway). Then save the resulting file somewhere safe, customize the variable org-export-odt-styles-file to the path to that file, and you're done.
I only write this because I had a little trouble figuring out how outline numbering works in openoffice. It would be pretty cool if the org option num: had an effect here, but I think that would require some work to implement (you'd have to have org override settings in styles.xml, presumably introducing the possibility of various errors).
