Yes, I have. I think it's the easiest way to publish an ebook because it covers all the ebook formats except Kindle, and it will get your book listed at Barnes & Noble, iTunes,and the other big ebook sellers.
You can publish in Kindle format through Amazon and you've got all bases covered.
Mind you, don't expect Smashwords to sell your book for you. You have to work out how to market it yourself - no one is going to find it if you don't let people know it exists. But then, that's exactly the same for ALL ebook publishers. Even the ones who claim to market your book for you, actually do very little.