On the many, many words on gutvol-d recently about poor results with auto-conversion from HTML to other formats (epub and mobi, among others): this is often due to choices that producers make about using HTML to impact layout, rather than just structure. Enough said.
Well, I think I work extremely hard to avoid using HTML to "impact layout", AND I work very hard to create HTML that will render "identically" in EPUB and MOBI, AND I check my work using a local copy of epubmaker, AND I check my work on multiple copies of physical EPUB and MOBI devices, YET still I find that I end being disappointed in the EPUB and MOBI that ends up being posted on PG from my well-intentioned efforts. Funny how pushing on one end of a rope doesn't lead to satisfying control over the other end of the rope. Again, if you allow posting in RST or TEI, why not allow posting in EPUB? EPUB comes much closer to being "a real complete book" that HTML ever will. And it's much easier converting EPUB back to HTML than trying to convert HTML to EPUB. And EPUB goes straight into Kindlegen to make MOBI and now KF8, with KF8 being in practice very similar to EPUB.