Recently one of my fellow LDStorymakes Authors Incognito members announced that he was putting an ebook out. The word got out and he ended up selling some before it was actually meant to be promoted. (which is today, actually...check it out! Yeah Darvell!)
I had a similar experience, though nothing has happened since the initial perusal, (sigh) though I haven't really gotten it out to Amazon and stuff -- anyway. It brings up the question, how do you promote an ebook? It's not like you can put posters up at the book store saying you're having a book signing... It's also kind of hard to sign a ebook. "Hey, can I sign your _____?"
Promotion has been the bane of many an author's life. It's one of the reasons publishers have been the draw instead of self publishing or becoming an 'indie' author. When you get picked up by a major publisher, they do all that ground work for you. They do the big ad sales, the pushing out to the bookstores, etc. When you do it yourself, then you are it.
One of my writing friends published a book himself several years ago. (Not an ebook.) He spent a lot of time going to various bookstores promoting his book; going to tourist stores and getting them to place it, and all the signings he could talk someone into. He managed to sell all his first run and go to a second run. He even had it picked up by an agent -- only to have them drop the ball. It's a great book, and I think the ebook version of it has sold well too. But he'll be the first to tell you he's earned every penny he's ever made, and he hasn't made himself a millionaire from it either.
Needless to say we don't go into writing with the idea that we're going to become the next J.K. Rowling, or at least the more intelligent of us don't. ;) I guess some people think their work is that good on the outset, but I know mine takes more work. I also think that how your book is promoted is something you need to think about in the contemplation of how you want to publish. Which do you want to do most? The foot work or the hand work?
First you have to finish one to get to that point. Keep up the writing.