Tristan King reports experimenting with Amazon’s KDP Select Program, a new system on the Kindle Store which increased his book’s sales over 600% within one week. Read his blog post here:
I also enjoyed a huge number of downloads the first time I tried KDP Select (back in Fall 2012), and it helped launch awareness of my book "How To Make Easy Money Selling Your Old Used Books On Amazon." Since then, sales have been steadily rising.
Other titles I tried with KDP Select didn't fare as well. But, since my ebooks are all in the non-fiction category, I think this skews the picture. I do believe fiction ebooks -- mainly fantasy fiction and mysteries -- benefit greatly from the KDP program, especially when the author has a series of books which center around one character. The freebie tends to work as a 'free trial' and if the readers like it, they tend to buy the other Kindle books in the series.