Both times I ran KDP promo days I saw a big jump in sales and made it onto the Amazon's bestselling list for several days, which I discuss here http://marktullius.com/2012/11/how-i-explained-the-number-of-kdp-fr...
Originally I thought the increased sales were do to something with Amazon's algorithm, but now believe it has much more to do with all the ads I put out, the majority being free and listed in the post. People continue to see the ads after the free days have passed and may decide to purchase it. I also think that it's more difficult to get people to download for free on smashwords, which I attempted. Having the extra step of having to sign up is enough to discourage some people.
I've also discovered that I had far more sales following a simple post on ereadernewstoday where they get a percentage of each book purchased through their link. This was when I had the book priced at $0.99 but I believe they include books up to $4.99.
I won't be using KDP for Brightside again, but may use it for my next novel in hopes that it encourages new readers to purchase Brightside. Hope this helps and good luck with your novel.
When I give a book to someone to read (usually the person has evidenced interest), I ask them to share it
with another reader. That way, I can hope the book will be passed around and, maybe, someone will buy
his/her own copy!
When I e-pubbed my books earlier this year, I did both of them Free on Amazon/Kindle, the 2nd one I also did Smashwords in conjunction with the Amazon/Kindle Free days. While on the free days, I did see a jump in status. My book was in the Top 100 for Kindle/Fiction. I did get a few sales for the two months after my debut but I marketed! I was doing book blogs interviews, guest blogs, I even enlisted a book-tweeting service while the first book was on Free days to get the word out about my free book (Mark is TOTALLY right about this part!). With all of that work, I sold only 4 books in 2 months through Amazon and a few more through Smashwords and B&N. I had over 200 downloads of my book. From what I'm seeing here on Book Blogs, that's not normal for a free book. More normal is 1K downloads. However, I am an unknown indie writer so the work is in getting myself known and creating buzz. Hence the groundwork of getting your name out there in some kind of niche circle prior to publishing -- if that's possible.
Once you have readers that like your work, they will talk about it and share it. But, your product has to be compelling to your target market for that to happen.