It depends on what you call 'publishing on Amazon'. I refuse to use CreateSpace because of Amazon's VERY sketchy manipulation of the contracts for writers and small press publishers. Amazon has proven time and again over the past 5 - 7 years that they are no friend to writers and small presses. Unfortunately, greed appears to have overtaken them.
That said, with Kindle dominating the ebook market, writers and small presses are forced to play the Amazon game. Selling handfuls of books is about where I'm at. I do have one author who is getting a lot of attention in NY and her Kindle sales are bumping up a bit, and her book is priced at $8.99. Most of the other Kindles I have are priced in the Amazon 'greed zone' of $.99 and $1.99. That said, we've been pushing the Nook for the lady in NY and her sales are almost dead even with Kindle.
I am not a fan of Smashwords personally. I keep hearing whispers of calamity with them, but then they keep right on trucking. I have nothing to base my opinion of Smashwords on other than wrestling with their instruction manual a couple years ago and then saying the heck with it.
I personally write fiction, non-fiction and poetry. Our authors are mostly non-fiction. As far as Amazon goes, I have seen too many of their underhanded manipulations behind the scenes to be too happy about them. Of course, when you're as big as they are, I suppose you get to throw your weight around. I just feel it's unfortunate that a company that started out writer-friendly has fallen prey to the almighty dollar.
Beware of CreateSpace. Amazon uses their own ISBN and I would look over the contract VERY closely and see what all you give up. I believe writers are much better off finding a reputable small press or setting up their own small press to help insure 1) that they keep their rights - especially all subsidiary rights and 2) that you can have some control over the retailer discount price, which Amazon inflates to their advantage.