I've been messing around with my epub creation script, and the thing's working pretty well at this point -- feed it a manifest file with some metadata in it, along with the files to be stuffed into the book, and it works just fine. Very cool. Most of the heavy lifting's done with some perl modules
Of course, actually building the ebook's the easy bit. Building a book that iBooks likes is the tricky bit, since it very sensibly assumes that you're only going to hand it ebooks it likes, and those books aren't going to change once you hand them off. If either of those things isn't true then it gets all sorts of cranky.
I'd like to bitch about that, I really would, but it's not really reasonable to do so. It's not a development tool, and treating it like one doesn't work too well.
For example, if you've handed iBooks a book that doesn't validate for some reason, or has an error in it, it'll yell. That's fine. But... if you fix that error, drop the new version of the book in iTunes and re-sync? Nothing happens. iBooks doesn't notice that a book's got new contents and happily re-displays the old contents for you, complete with errors. You have to delete the book, sync, re-add the book, and resync. All with iBooks running, or it doesn't reliably clear out its cache. Yech.
And lets not even get into the execrable HTML that Word, OS X's RTF->HTML methods, and various publishing tools create. They'll all happily ladle on vast amounts of crap that generally need to be stripped away if you want to make a simple ebook. Stripping that out's been huge amounts of fun, especially coupled with iBook's double-sync quirk. Thankfully there's http://www.threepress.org/document/epub-validate/ to do validation, but that only works if you're online, and doesn't catch formatting problems, just HTML issues. (Which, granted, is a big help)
All this'd be so much easier if there was an OS X version of iBooks I could work directly with. All the ePub capable ebook software I've got handy on my mac is altogether too forgiving (or, in the case of stanza, outright ignores a lot of stuff, which is nice as a reader but a pain in the neck for figuring out if things are working)
Ah, well, such is life. I think this thing is about ready to release for other folks to play with.