"The pros of this program are immediately apparent: the interface is rather DIY friendly, the icon design seemed crisp and best of all the creation of the TOS (Table of Contents) couldn’t be simpler. One merely highlights the chapter heading as an h1 or h2 (or any ‘h’, really) for each chapter, then hit a button and “voila!” the beautifully-linked chapters appear in a list on the right hand side, glowing in their success and all ready to be tested. This contrasts to the more involved, coded approach that users of Calibre have struggled with, sometimes abandoning their TOS altogether."
I find the TOC feature a bit annoying when I try to tweak a published book that doesn't use this standard. There is still way too much non-standard and simply stupid implementation of HTMl and CSS to create an ebook so an application that assumes some type of sanity in an ePub is limited in what it can do.
Overall the Calibre ePub creation is very good for converting existing content into ePub. Where Calibre stands out is the WYSIWYG editor intelligently coupled with the nuts and bolts ePub components creation and publishing.