Ya know, after playing with this a bit more, I think I can actually write a script that will, using a default formatting design, create a ready to use ebook in Epub format just by copying and pasting text into a loader file. The script then reads the import text, breaks it up into sections, and then spits out the entire epub's contents in one motion.
After analyzing how each of the files in the epub works, it should actually be quite easy. All you'd need to do is enter a few details, and you're golden. In fact, with PHP5, you could actually create a complete web script that would even zip up the contents for you. All you need to do is make sure your text is formatted properly beforehand (IE, ensure that you have something like <break> to mark the breaks between chapters, and then let the script do the rest.
It'd ultimately be faster than Sigil, despite how nice it is, even though it's in early beta.
If someone wants, I could actually write a script that does that. IE, instant epub for just a few minutes of work.
It won't be all fancy, smancy, but it'll still look nice. Plus I'll open source the script in case someone wants to tinker with it a bit.