There's a lot of bilious ire directed at this software in the comments, which is misplaced. Yes, it's expensive. Yes, you can use other software or hand-code the things yourself if you want — and I've done both of those in the past. But if you need to semi-regularly produce attractive it-just-works ebooks in a variety of formats, then Vellum is exceptionally good and a massive time-saver.
I can produce a perfectly-functioning ebook in multiple formats from a Word file in about twenty minutes using this software, depending on how many import glitches arise from the original doc. There is no other piece of software that comes remotely close to that speed or ease of use. When muttering about the cost, factor in your own billable time. When you do that, Vellum very rapidly pays for itself even at an admittedly high price.
The developers are responsive, and constantly adding improvements. It's also rock solid as a piece of software — a professional tool that's FAR easier to use than any of the alternatives. I'm giving it 4 stars because, sure, I would have loved to have paid $99 instead. But for fast, reliable and WYSIWYG creation of ebooks, there's nothing like it.
If the price isn't worth t to you, fine — don't buy it. Hand-tool your books, and deal with the problems caused by multiple formats and idiosyncratic HTML. But don't trash Vellum until you've spent a while working with it.