eBooks make self-publishing much easier. Both print and ebooks offer formatting challenges, but in the print world, the truly hard part is getting the books where readers will see them. You can use a print-on-demand (POD) service, of course, like Amazon's CreateSpace, but the problem is the books are sold only online (or by you, if you are willing to buy them and resell them) and you can't price them any cheaper than traditionally published books (often sold at a discount!) without losing money. Some day there will be POD machines in every bookstore and it might be worth it to self-publish in print, but right now it's an iffy thing.
eBooks are still iffy, of course, in that you're never guaranteed success. But the distribution channels are easier to manage with ebooks partly because all ebooks are sold online, not just self-published ebooks. Also, Amazon and Barnes & Noble both offer easy-to-use self-publishing platforms (KDP and PubIt, respectively), as does Smashwords,
Smashwords is unique (to the best of my knowledge) because it is a retailer that sells only self-published books and because it offers three major advantages over the other DIY publishing platforms,
The first is that aside from Smashwords itself, once your book is loaded there, it offers the opportunity to push it out to other retail platforms, specifically (as of now) Sony, Kobo, Barnes & Noble Nook, Amazon Kindle (although this does not seem to be fully implemented), Diesel, and Apple iBooks. It's true that Amazon is still the gorilla of ebook sales, but all the other platforms added together can make it worthwhile to pursue this option.
The second advantage of Smashwords is that, unlike KDP and PubIt, Smashwords lets you make your book free, either by offering a code for downloading or just by making the price zero. Further, once you have done that, some (but not all) of the other retailers will also make the book free.
Making a book free might not seem much of an advantage. You could post a book on your own website and make it free to download, after all. But readers troll the online stores for free ebooks, and if you have more than one book, giving one away for free can get you sales on your other books (especially if the free book is the first in a series).
The third advantage of Smashwords is they make your book available in multiple formats, without DRM. Surprisingly, that's related to the one disadvantage of Smashwords. They require a Word file be loaded that corresponds to their guidelines and then they convert that file to the other formats they offer, and this gave the writer less control over how the book looks in the downstream retail outlets. However, Smashwords recently announced they plan to start supporting ePub uploads, so that might help because the other retailers will want ePub.
Perhaps because they only sell self-published works, Smashwords actually reviews each book that is uploaded, not for editorial quality (now there's a loaded term!), but for formatting. They make the distinction of having a premium catalog, and only well-formatted books are assigned to it. Your book cannot be pushed to major retailers like iBooks unless it is in the premium catalog (some retailers also require an ISBN).
In many ways, Smashwords acts more like a publisher than the other platforms; when they push books to other retailers, their name appears as the publisher of those books.
In the eight months since I started publishing, the one platform that has been a total disappointment has been PubIt; unlike Amazon, I don't think Barnes & Noble treats self-published books the same as traditionally published books. Ergo, I recently decided to pull my books from PubIt and use Smashwords to sell on Barnes & Noble. This will provide me considerably less swift feedback on any sales, but I would rather have slower feedback and more sales. I'll post about the results of this experiment after a while, but I'm not taking the books down from PubIt until Smashwords has shipped them to Barnes & Nobles, so that might be a few weeks.